You do not expect Robert De Niro, in person, to be funny.

If you have admired his gift for playing characters who walk on the dark side in dramas such as Cape Fear (1991), Raging Bull (1980), The Deer Hunter (1978), Taxi Driver (1976) and The Godfather: Part II (1974), which each earned him an Oscar, it is startling to see him in something more light-hearted.

And this is despite the fact that he has proven his chops with the hit comedies Meet The Parents (2000) and Analyse This (1999).

But Life and other reporters find the star - who is known for being reticent with the press - in an uncharacteristically chatty, smiley mood as he promotes his newest comedy, The Intern, in New York.

The movie - which opens in Singapore tomorrow and casts him as a retiree who interns for the young founder of a clothing company (played by Anne Hathaway) - is the latest in a string of comedies for the actor, who seems to have gravitated towards the genre in recent years, in titles such as Silver Linings Playbook (2012), Grudge Match (2013) and Last Vegas (2013).

The 72-year-old says this was not a conscious strategy. "No, things just came the way they came," he says. For example, Analyse This - in which he played a mob boss forced to see a psychiatrist after getting panic attacks - happened because he wanted to work with comedian Billy Crystal, he explains.

"He had a fun idea for me to play this character and it was just a thing I was curious to do. I thought it had funny stuff in it and I liked the idea of making fun of the characters like the ones I've played before - of turning them upside down and making fun of the whole situation.

"And that's where it started."

In terms of acting technique, comedy is not that different from drama, either, although De Niro concedes that it can be less emotionally torturous to get into character for the former.

But "in other ways, it's just as difficult, or just as much of a procedure, if you will. It doesn't change in a lot of ways".

Asked if he is funny in real life, his face crinkles into a smile. "My mother used to say I was funny," he says, chuckling.

Still, it continues to have major shock value whenever he publicly displays a sense of humour, as he did when he delivered a commencement speech to arts school graduates in New York a few months ago, telling them: "You made it - and you're f**ked."

His point was that many of them had chosen a field, show business, in which it will be difficult to find jobs - just like it was for De Niro himself when he was in his 20s.

"It wasn't easy for me, I started out like everybody else - looking to get into something, sending out resumes and auditioning, reading the trades and going to open calls.

"I was also lucky that I got into one movie and then something else, and here and there."

He adds that he was fortunate that one of the first directors he auditioned for was Brian de Palma, who put him in his first starring role, the comedy-drama The Wedding Party (1969), and would go on to direct him in the gangster flick The Untouchables (1987).

"But yeah, it wasn't especially easy for me. Which was pretty much typical for a young actor trying to get into the business.

"I never thought I'd get this far."

Today, De Niro has starred in, produced and directed more than 90 films and is widely regarded as one of the most gifted actors of his generation.

Retirement, he says, is not something he understands, not for himself anyway.

"Some people retire, I guess, because they have to, with the job they have. In my case, I have too many things I want to do and, knock on wood, I'm in good physical shape, so I can follow through on things," says the actor, who has been married twice and has six children aged three to 44.

His youngest child - his daughter with wife Grace Hightower, 60 - was conceived with a surrogate in 2011, making him a father again at the age of 68.

"I think if you retire, you stagnate if you don't have something to do - unless you enjoy doing nothing. And some people do, you know - playing golf, going around and visiting all their grandkids," says the grandfather of four.

"And there are people who become very active - they travel around, they do things they never could do while working. You have to keep busy, obviously - there's no point to living if you're not going to do anything."

In The Intern, his character, a widower, decides to come out of retirement and finds himself in an office with much younger co-workers, who initially underestimate him because of his age.

Such ageism can happen to even a big Hollywood star, the actor says.

"Maybe it's me thinking the grass is greener in other countries, but here, youth is a very important part of the culture. Age is not as revered, if you will, as it is in other places.

"To be in a movie, they would prefer you to be young and pretty or young and handsome. And if they could have cast me in this part as a young man - in other words, if they could cast my character, Ben, as a 32-year-old Brad Pitt - they'd rather do that," he says with a laugh. "They'll make it work!"

Ultimately, he adds, it is up to the movie-going public to decide whether there will be more roles such as his 70-year-old character in this film, who is the protagonist and has a love interest, played by Rene Russo, 61.

"If the movie works and everybody sees it, then they'll be more interested in making other movies like that. It's that simple."

• The Intern opens in Singapore tomorrow.