At 68, his hair and beard now almost completely silver-grey, Francis Ford Coppola looks like Fidel Castro's jollier younger brother. He is holding court in an expansive hotel suite in Rome which looks out over the Spanish Steps and the dome of St Peter's beyond. We are here to discuss his new film, Youth Without Youth, his first in 10 years, but the talk has turned almost immediately to the melancholy subject of growing old.

'At my age,' he says, 'you start to think about stuff you didn't think about before. One of the big questions that keeps coming up is "what if?" What if I'd done this instead of that? What if I'd become the experimental, avant garde film-maker I always really wanted to be?'

Well, for a start, I say, you wouldn't have made The Godfather. Or, for that matter, Apocalypse Now. And you wouldn't now be regarded as one of the greatest directors of the 20th century. 'I guess not,' he says, sounding not that worried one way or another. 'But, I would have made more personal films. Films of ideas. Like the guys who were making movies when I came of age - Godard and the New Wave. Which is what I wanted to do in the first place.'

Why didn't he, then? A long sigh. 'I became successful in Hollywood,' he says finally. 'I got sidetracked.'

He says this with wistfulness rather than deep regret, but it is still an astounding thing to hear from one of the great masters of 20th-century American film: the sense that he considers himself to be artistically inferior to a chancer like Godard. Now, though, as if to assuage this long-held regret, Coppola has finally got to make an experimental film.

Youth Without Youth is based on the philosophical novel of the same name by Mercia Eliade. It stars Tim Roth as Dominic Matei, an ageing Hungarian linguist who, having made preparations to commit suicide, is struck by lightning on a street in Bucharest on Easter Sunday, 1938. Like Christ, he rises again, and, while recovering from his ordeal in hospital, his body mysteriously begins to regenerate. His youth returns, but he retains the memories and regrets of an old man, and is haunted by the long-lost love of his life, Laura, played by the wonderful Alexandra Maria Lara.

'I was on holiday on a beach when he rang me up,' says the young actress, who has previously played Hitler's secretary in Downfall and Ian Curtis's mistress in Control. 'I was so shocked, I immediately cut him off just so I could compose myself. But he was so generous in his way of working. It's a complex film in many ways but he was very patient with all my questions and talked me through the most demanding scenes. I kept thinking, "This can't be happening to me, I'm working with a legend."'

Youth Without Youth is a film that forgoes thrills and spills for endless rumination. Its pace is slow and stately, its tone regretful. I put it to Coppola that today's cinema audience may find it demanding.

'Well, it's essentially a fairytale and, as such, it's not that hard to understand,' he replies, sounding slightly testy. 'I guess it may appear weird to people who want me to make The Godfather or Apocalypse Now over and over but, you know, when Apocalypse Now came out, everybody said, "Wow, this is so weird". That was the initial reaction almost across the board. It took five years really before they stated saying, this is not so weird. This is just different.'

Coppola has travelled to Rome for the city's annual film festival, and it is clear that the Italian-American director is revered here. The following day Youth Without Youth will receive its world premiere. He has brought the entire Coppola clan along with him: his wife, Eleanor, a documentary film-maker who made the brilliant Heart of Darkness about the fraught filming of Apocalypse Now; his daughter, Sofia, a celebrated director in her own right (Lost in Translation, Marie Antoinette); and his son, Roman, who co-scripted Wes Anderson's The Darjeeling Limited. (Another son, Gio, died in a boating accident in 1986.)

'It's a family affair,' he says, smiling. The celebratory atmosphere has been punctured, though, by a story that has just broken in the press in which Coppola seems to accuse Robert De Niro and Al Pacino, who both starred in the Godfather films, of growing old and lazy and 'living off the fat of the land'. One headline reads: 'Coppola launches blistering attack on three of the biggest stars in the film business.' Another claims: 'Coppola mocks Godfather stars.'

On the page, the quotes look pretty damning. Of the man who played Michael Corleone, Coppola is quoted as saying, 'Pacino is rich, maybe because he never spends any money; he just puts it in his mattress.' Even Jack Nicholson gets it in the neck for having a 'mean streak' and being 'always wired in with the big boys, the big bosses of the studios'.

Coppola shrugs. 'How outrageous,' he says. 'And how funny. I mean, it's not so much what I said, which is what I would say to them, it's that it's been taken totally out of context. It was wrapped up as if I was attacking them. I didn't attack them. I love and respect and admire them. The headlines were, "Jack Nicholson is a waste of talent". I mean, what kind of schmuck would say that?'

So, what happened, exactly? 'Well, right at the end of a long interview, this guy from CQ [sic] magazine asked me what I thought of them. And I said, well they're not the same guys they were when they were young and hungry. Now they are rich. Deservedly so. Thank God, you know. Then it all gets twisted. I mean, I'm a friendly guy, right? You ask me this or that, I'll tell you.'

So, for the record, what do you really think about them? 'What do I think of Bobby De Niro and Al Pacino? Well, for a start, I don't feel I made them, I feel they made me. That's how highly I regard them. And Jack is a huge talent, one of the greats. These are my friends,' he says, sighing. 'And that kind of stuff can hurt friendships.'

As he approaches 70, Coppola seems oddly vulnerable. It is not just that the avuncular and effusive gentleman sitting on the sofa opposite me bears only the slightest resemblance, physically and temperamentally, to the driven, larger-than-life character who made those grandiose American films in the Seventies. It is more that, even as his legend has grown, the movies he has made since then seem to have mattered less and less.

It is 10 years since his last film, The Rainmaker, a solid, well-crafted take on a John Grisham thriller. It was not a commercial success. Neither was Tucker: The Man and His Dream (1988), nor Gardens of Stone (1987) nor the entertaining but oddly empty Fifties period piece, Peggy Sue Got Married (1986). They were all perfectly well-made films but lacking in greatness, devoid of the visionary scope and bravura direction of his great early masterpieces. You have to go back to the early Eighties to the likes of One From the Heart and Rumble Fish to catch a glimpse of the greatness that was announced so dramatically a decade earlier with the first two Godfather films.

Of late, too, it has often seemed that Coppola was more content to tend the vineyards on his vast California estate than make movies. (He has two wine companies situated in Napa Valley, one small and traditional, the other big and globally successful, as well as a thriving pasta company in Brooklyn.) Having bought the legendary Inglenook Chateau in 1995 with the £4.5m profits from Bram Stoker's Dracula, he is now using some of the vast fortune he has made from his vineyards to make films.

'Everything is genre-driven these days, and that's not what I'm interested in. Some of the greatest directors we have get sucked into returning to the same subject matter, and essentially making the same film over and over,' he says, perhaps referring to his friend, Martin Scorsese. 'Whereas I'm in the fortunate position of having become wealthy though the wine business. That is the reason I am able to make the films I want to make.' How much did Youth Without Youth cost, then? He pauses. 'I can't tell you exactly but, let's put it this way, I can make any film I want for around $20m (£10m) or less.'

The film was shot on location in Romania with a small crew. Coppola insists this was because he wanted to make it the way his younger self would have made it had he not been 'side-tracked' by Hollywood.

'I very consciously tried to make it the way a student film-maker would. I put all the equipment in a truck and went to Romania. I didn't have any of the great collaborators that I've had the pleasure of working with in the past. In fact, I worked with a 28-year-old local cinematographer. Which was kind of apt because I felt like I was a 28-year-old director all over again.'

This, of course, could simply be Coppola putting a brave face on things. Another way of reading it is that his commercial cachet in Hollywood is now so low that self-financing his projects is the only way to get them made. Whatever, he seems remarkably calm about it all, even mellow. This is after all a man who, while recreating the excesses of the Vietnam war in the jungles of the Philippines for Apocalypse Now, collapsed on the set just after his lead actor, the young Martin Sheen, had a near fatal heart attack.

'Oh man, all that stuff was exaggerated, greatly exaggerated,' he says, not altogether convincingly. 'I read the other day that I had three nervous breakdowns. I maybe had one little one. And that was through smoking, not overwork. But three breakdowns, I mean, come on!'

Nevertheless, his younger self seems close to meltdown more than once in Heart of Darkness, his wife Eleanor's documentary, which I watched again recently. I also reread her great book, Notes, on the making of the film. In it she writes of her husband's collapse: 'Francis said he was as near to death as he has ever experienced. He said he could see reality coming down a dark tunnel and he was totally scared that he wouldn't get back.' Was she exaggerating, too?

'Well, Heart of Darkness is obviously accurate,' he concedes.. 'I guess I was a little - what's the word? - manic back then.' He chuckles like a guilty child. 'Then again,' he says, 'you have to be manic to get through something like that.'

One of the funniest and most revealing anecdotes in Eleanor Coppola's book describes a row she had with her husband in the driveway of their San Francisco house when the making of Apocalypse Now had all but taken over his life. They were shouting at each other across the roof of their car when their daughter, Sofia, who was just a toddler back then, wound down the window and yelled 'Cut!'

Now Sofia is a successful director in her own right, as calm and laid-back on set as he was histrionic and overbearing. 'Sofia has a signature,' he says, proudly, 'We call it terroir in the wine business. You would know you were watching one of her movies even if you hadn't seen the credits. I hope it's the same with me.'

I wonder, though. For all his greatness, Coppola's movies are not really united by a signature style. It would be difficult without prior knowledge to guess that Youth Without Youth - or, indeed, Peggy Sue Got Married or Rumble Fish - was directed by the same man who made The Godfather. He once described himself as 'a sloppy filmmaker'. What exactly did he mean by that?

'Well, making a film is like cooking a dinner. I guess I'm a sloppy cook because I do it out of enthusiasm, essentially. I don't measure everything but I have a good feel for food. Same with movies. The bottom line is I'm emotionally sloppy. That's why I need a great cinematographer. They're the opposite of emotional and sloppy, they're precise. You need both to make a good film.'

Does he still enjoy filmmaking as much as he did when he was younger and bolder? 'Well, it takes longer these days. I do other things now as well - it's not just one film and then another.'

Someone - it may have been Werner Herzog - once said that making a film was governed by fear. Does he agree? 'Oh, yeah. Every day you are in a total state of fear. It's one of those jobs where you go ahead in an attitude that would probably stop other people from going ahead. That's the nature of it.'

His next film is called Tetro and stars Javier Bardem. 'I want,' he says, 'to make a great old-fashioned movie with Elia Kazan-style acting.' He has written the screenplay himself and will soon be taking his truck of equipment to Argentina to begin shooting. 'It's about fathers, sons and brothers, a bit Tennessee Williams, a bit Rocco and His Brothers.' He pauses for a moment and looks out across the domes and spires and red-tiled rooftops of Rome. 'I guess the way it has turned out is that when people go to see a new Francis Ford Coppola movie, they hope it's going to be another Godfather. There is always that hope even in the face of the impossibility of that actually happening.'

That's quite a weight to carry, but by acknowledging it you sense that Francis Ford Coppola has finally made it lighter. The twinkle in his eye when he talks about Tetro makes me think that he may yet surprise us. I really hope so. As he has grown older, cinema has grown safer. 'For a movie to be great,' he says just before we conclude, 'someone has had to have taken a risk. If no one is willing to do that, the movies will not be good. That much I do know.' He seems ready to take that risk at least one more time.

A life in pictures

1971

Patton

Biopic of the controversial Second World War general - wins Oscar for Best Screenplay

1972

The Godfather

Winner of three Oscars including Best Picture and Best Actor (Marlon Brando)

1974

The Godfather Part II

Wins six Oscars

1974

The Conversation

Surveillance expert gets involved in a murder plot

1979

Apocalypse Now

The nightmare production story of this Vietnam War epic is almost as famous as the film itself

1982

One from the Heart

This ambitious musical was Coppola's first major flop

1983

Rumble Fish

Matt Dillon and Mickey Rourke as street fighting men

1984

The Cotton Club

Prohibition speakeasy musical drama

1986

Peggy Sue Got Married

Time-travel comedy starring Kathleen Turner

1988

Tucker: The Man and His Dream

Jeff Bridges as auto pioneer

1990

The Godfather Part III depicts the later life of Michael Corleone to less acclaim than its predecessors

1997

The Rainmaker is a conventional courtroom drama based on a John Grisham tale that sees an idealistic lawyer up against a corrupt corporation

· Youth Without Youth opens on Friday