He is a prolific artiste who has appeared in more than 350 films. But Shigeo Tokuda gets little in the way of recognition on the streets of Tokyo. Perhaps that's because at 77 he couldn't look less like a star. Or perhaps it's because admirers tend to keep their appreciation of his work to themselves.

Tokuda has shot to prominence as Japan's oldest porn actor, the unlikely face of a brand of Japanese blue movie that taps into the country's fast changing demographics. And yet he didn't even get started until he was almost 60.

Tokuda, who is married with two adult children and a grandchild, made his debut in 1994 after a meeting with a porn director in Tokyo.

"I was a fan of adult films and went directly to his office to ask if they'd got specific films in stock," he says. "He asked me there and then if I wanted to appear in a film. I immediately said no."

He soon changed his mind and at 59 in a hotel in western Tokyo he launched his acting career, playing the part of a company president with a roving eye.

"It was my first time, so they made sure there weren't too many people on the set. I held the camera myself, and the only other people in the room were my co-star, and the lighting and sound engineers."

So began his double life as a travel agent by day and a porn actor during downtime.

Other than changing his name – Shigeo Tokuda is his professional alias – his attempts to conceal his acting career from his family are surprisingly half-hearted. He had to confess to his daughter after she intercepted a fax offering him a scene that left little to the imagination. "She was speechless for a while," he says.

He had already told his wife of 45 years that he played bit parts in films that sometimes included pornographic content. "She occasionally suggests it's about time I quit, but we have never argued about it. As long as I don't bring up the subject and treat it more like a hobby, I can get away with it. But I have never breathed a word to my son."

The director who gave Tokuda his break was ahead of his time. In recent years, films featuring male and female actors in their 60s and 70s have made a sizeable dent in Japan's huge adult film market.

According to industry executives, the market for "silver porn" has doubled over the last decade and now comprises about a fifth of the 3,000 adult films, worth 100 billion yen (£825m), that Japan produces every year.

That growth reflects wider social changes in Japan, where more than a fifth of the population is 65 or over. That figure is expected to rise to about 40% by 2055.

The impressive life expectancy of the Japanese – 86.4 years for women and 79.6 years for men – has spawned a range of services for the elderly, from tailor-made exercise parks in playgrounds once meant for children to bigger, easier-to-read fonts in national newspapers.

The elderly now dominate traditional industries such as fishing and agriculture; the average age of a Japanese rice farmer, for example, is 66.

The spread of free internet porn has expanded Tokuda's fan base beyond Japan's borders, including the sales of titles in the US.

But, according to film producer Gaichi Kono, the industry is struggling to survive the switch from DVD format to online distribution.

"If anything, Japan made too many films in the past," says Kono, who has also acted in about 1,300 adult films. Japan, he adds, has been frustrated by strict domestic censorship laws that require genitalia to be digitally obscured.

"People prefer to watch uncensored material on theinternet, and that has contributed to the tough times we're seeing in the Japanese porn industry.

"Before, a top actor could earn 1m yen for a day's work. These days, the pay is nearer 100,000 yen to 150,000 yen for a properly produced film."

Kono attributes the genre's popularity to the feeling of affinity viewers have for actors who are past their physical prime, even if the storylines are the stuff of pure fantasy.

Tokuda usually appears with much younger women – the youngest was 54 years his junior – in films with such titles as Forbidden Elderly Care.

He finally quit his travel agency work six years ago after suffering a heart attack. Late last year, he began to feel discomfort and had bypass surgery in August.

Yet he is already preparing for his next film, to be shot in an as-yet undisclosed location on Friday.

"When I know the location, I'll turn up and meet the actress," he says. "We'll have a chat so we know if it's going to work out or not."

What would his doctor make of a return to work so soon after having heart surgery?

"I told him that my work sometimes involves being on the set of porn films and that I occasionally perform 'manual labour'", he says with a laugh.

"But he didn't tell me to quit, just not to do any heavy lifting and to take plenty of rest. And he didn't warn me about getting over-excited. In any case, my blood pressure is normal. If possible, I'd like to keep doing this until I'm at least 80."