Occupying the corner table of a near-empty cafe off Sunset Boulevard, Alfred Molina eats porridge as he mulls the implications of ageing in Hollywood. “I’m getting older now. Certain roles are beyond me. If someone says we’ve got a great part for you but you’ll need to lose 30lb, I say, well, get a thinner actor.”

He pats his stomach and gives an affable shrug. “Same thing if I was asked to gain 30lb to play Orson Welles. I’ve done physical transformations in the past, but not any more. You notice that it’s mostly young actors who do it.” He pauses. “I’ll be 62 this year.”

Molina wears the years well. Full head of glossy black hair. A hint of jowl around the stubble, but alert eyes and few wrinkles. Bearish physique. Looks after himself. Even so, when it comes to action films, he makes his preferences clear. “I tell them, get the young ones to do the running and jumping, and I’ll do the shouting and pointing.”

He laughs, a hur-hur-hur gurgle-chortle. During a varied career, spanning blockbusters such as Raiders of the Lost Ark and Spider-Man 2, and artsier fare such as Letter to Brezhnev and Chocolat, Molina has won a reputation for flair and versatility. The London-born actor, son of working-class Spanish and Italian immigrants, switches accents and roles with ease, a facility described with typical self-effacement: “I do good foreign.” One variable Molina cannot tweak, however, is time.

It is a recurring theme as we munch breakfast on a misty Los Angeles morning. Tousled in jeans, lumberjack shirt and parka, he apologises for having arrived a few minutes late, and over the next two hours discusses his two decades in Hollywood, the nearly three decades between two seminal gay roles, and the ravages of time – in particular, of Alzheimer’s – on the love of his life, Jill Gascoine.

In his new film, Love Is Strange, which opens in Britain in February, Molina and John Lithgow play a New York couple who have been together for 39 years. When they take advantage of a law allowing them to marry, Molina’s music-teacher character is sacked from a Catholic school, shredding the couple’s finances. They sell their gorgeous apartment, and lodge separately with friends, precipitating a bittersweet meditation on love, friendship and belonging.

“This was a story at the complete opposite end of the Aids spectrum, where you so often see stories about same-sex relationships, where it’s young people finding each other and their way in the world, about promise and yearning,” says Molina. “Here we have a rather ordinary, late-middle-age couple.” Gayness was not the point. “Everything that happened to them could have happened to a straight couple ... this wasn’t an issues movie.”

It is a marked contrast to Prick Up Your Ears, the 1987 Stephen Frears film about the semi-clandestine relationship between the playwright Joe Orton and Kenneth Halliwell in homophobic 1960s England. It ends tragically when Halliwell, superbly played by Molina, kills Gary Oldman’s Orton, then himself.

“There was a lot more grungy sex in that, chasing strangers down the street, snogging them in the corridor,” Molina recalls fondly. Love Is Strange, in contrast, features gentle gents in a tolerant era. “There’s been a huge shift in gay politics and equal rights. Things have moved on tremendously. There’s still a long way to go, but that’s an amazing journey that we’ve made.”

Alfred Molina as Kenneth Halliwell in Prick Up Your Ears. Photograph: ITV/Rex

The two roles in some ways bookend the gay-rights struggle. Molina has stood on platforms promoting equal rights, but considers himself a “straight ally” rather than a crusader. “Prick Up Your Ears may be viewed in some circles as an iconic movie, but me personally an icon? No. Other people are much more visible and vocal.”

He does not think only gay actors should play gay roles, or vice versa. “Your sexual orientation is irrelevant in terms of playing the character.” That said, he cheerfully concedes it would have been more fun snogging, say, Helen Mirren, than Lithgow, an old (heterosexual) friend.

He likes that Love Is Strange focused on long-term love. “Love stories are often centred around the beginning, the discovering of each other. The other end of a long-term relationship is never viewed as particularly glamorous or sexy because it’s not about sex any more. When you’ve been with someone that long, it’s about companionship and security and comfort. But there’s an audience for these kinds of stories.”

Long marriages, he says, go through phases – sex, nesting, children, children leaving, empty nesting – and all the while the relationship evolves. “The things that would have enchanted you in the first year turn into small little irritations and then become enchanting again years later.”

And then, at some point, the body betrays you, or your partner. “It’s a love story about what happens when we get older and frailer and are less capable of fighting off the enemies, of fighting off adversity,” says Molina, sipping his second latte. He is referring to Love Is Strange but it could just as well be his own marriage.

He married Gascoine, 16 years his senior, in 1986. A successful actor in her own right, best known as Britain’s first female TV detective in The Gentle Touch, she moved with him to LA in the 1990s when his career took off on the back of Hancock, Enchanted April, Anna Karenina, Boogie Nights and Frida.

A solid marriage, by all accounts. In 2013, Gascoine revealed at a Beverly Hills fundraising gala that she had Alzheimer’s. “Things happen and you have to go with them, adapt,” says Molina, the voice, soft for his size, growing softer. “I looked after Jill at home for four years. It got to a point where I was doing more harm than good. The house became a minefield. So in the past year, she has gone to a care home. The Alzheimer’s has started to get radically worse.”

He pauses and gazes across the empty cafe, beyond which the mist slowly lifts. “She doesn’t always recognise me. She did when I visited yesterday. You see flashes of the old person. That’s the heartbreaking part. You see those moments. You long for them. But they come less and less.”

Molina with his wife Jill Gascoine in Los Angeles in 2012. Photograph: Amanda Edwards/FilmMagic

Molina has no plans to watch Still Alice, Julianne Moore’s Oscar-nominated turn as an academic stricken with the disease. “Much as I adore Julianne, I won’t go to see it. I don’t think I could bear it.” He goes quiet. “A lot of people are fighting the same battle as me.” There is no sign of self-pity, only sorrow.

Despite occasional blockbuster roles, notably the diabolical Dr Otto Octavius in Spider-Man 2, Molina says he needs regular work, taking on jobs such as Law & Order, The Da Vinci Code and An Education. “I’ve never been in a position where I could afford not to work.”

His career goal has always been simple: stay employed. “I got that from my dad,” he says, adopting a thick Spanish accent: “ ‘Real men don’t fight, real men pay their bills.’ ” The result is a “crazy quilt” oeuvre. “I’ll do anything. I’m a bit of slut that way. My problem is saying no.”

Molina regrets a few jobs – diplomatically declining to name them – but has no plans to retire. He enjoys the work too much. “Actors never die, they just become less available.”

Molina has steered clear of method-style immersion or, God-forbid, catharsis. “It’s not your job as an actor to feel anything. It’s your job to make the audience feel it. What you feel is neither here nor there. I don’t put myself through some terrible pain, or create anguish for myself. That’s therapy.”

As Dr Octavius in Spider-Man 2. Photograph: Allstar/Marvel

Even so, when obliged to “beat seven shades of shit” out of Sally Fields’s character in the 1991 film Not Without My Daughter he apologised before filming the scene. A true pro, she replied: “Well, you better give it all you’ve got or I’m going to beat the shit out of you.” He guffaws at the memory.

Notwithstanding the London accent and sense of humour, you can see why the director James Ivory once rejected him as “too ethnic” for a posh English role. Molina has been in Hollywood so long and played so many foreigners that on visits to the UK many express surprise that he is not a Yank. Gascoine used to speculate that was why the Guardian omitted him (but not her) from its birthday column.

In his next gigs, he is due to play an Afghan diplomat, then a Mexican-American lawyer and then, rather late in his career, a British aristocrat. The prospect tickles him.

An English nob. Congratulations, I say.

He claps his hands and cackles. “Ha! Recognised by the Guardian as an English nob. After all these years.”

• Love Is Strange is out in the US, released in London on 6 February and across the UK on 13 February