"It was like having a script from another world," Caine laughs. "I was amazed that he'd heard of me! I'm well known in England and America, but in Italy? But my agent said he wrote it for me. So I asked Paolo, 'Did you really write this for me?' The director replied, 'I wrote it for two of you, but the other one was busy.' That put me in my place."

Michael Caine and Harvey Keitel

Set at a Swiss health resort, the film is an exploration of how it feels to grow older, and Caine didn't hesitate when scenes required him to appear wearing only a towel. "It's the only body I've got," he says matter-of-factly. "At least it was a reality. Young people should know: this is what's going to happen, do don't get too smart about it." Was he tempted to hit the gym before those scenes? "At my age getting in shape is a waste of time," he says. "What you see is what you get. No one expects me to look like Brad Pitt!"

Even so, Caine has learned to take care of himself as he has grown older. "I drink less, I eat healthier and I want to stay reasonably fit for the sake of my three grandchildren," he says. "I live for them. And I don't mind playing elderly roles now because the alternative is playing dead people!"

And he has no plans to slow down at age 82. "You say you're going to retire because you think you're not going to find good roles anymore," he says. "And then you get a director like Paolo Sorrentino or Christopher Nolan who offer you great parts. So suddenly you're not retiring anymore. And I'm very grateful. I feel very fortunate to have lasted this long in the business, made some money doing it, and now I get to work for the pure joy of it, although I still like to get paid! But I loved this film. I'd have done it for free, but I didn't tell the producers."

Watch the trailer for Youth here: