Next Saturday Yoko Ono turns 79. In June she will come to London to launch a retrospective of her work at the Serpentine, which will include work she's making right now. "My work's getting better, I hope," she says. "If it's not, why do it?"
A keen tweeter – "it's almost like a haiku, but involving other people in a participation act" – Ono refuses even to recognise the concept of age. "Some people are old when they're 18 and some people are young when they're 90. You can't define people by whatever society determines as their age. Time is a concept that human beings created."
Ono is by no means unusual in defying the conventional wisdom that artists peak in early or midlife, then suffer a long fade into the sunset. This week 83-year-old Yayoi Kusama launched a career-spanning retrospective at Tate Modern, while Gerhard Richter, the gallery's previous incumbent, turned 80.
On Thursday the National Portrait Gallery opened its exhibition of Lucian Freud's portraits, featuring work he made right up to his death aged 88 in July last year. David Hockney's huge Royal Academy show, meanwhile, consists mainly of work he created after the age of 70.
Art critic Martin Gayford, whose portrait Freud painted, says the NPG show demonstrates that the artist's powers intensified rather than diminished with age. "He went up another level – in more or less every room until you approach the end he seems to have pushed a little bit higher.
"He painted Leigh Bowery about the time he passed 70 and his work shows a step change in scale and ambition. He had a feeling that it was now or never."
While visual artists have the late works of Rembrandt and Titian to inspire them, other art forms are more closely associated with youth. Yet Woody Allen, 76, has an Oscar nomination for Midnight in Paris and Roman Polanski, 78, received plaudits for his latest film, Carnage. Meanwhile, Leonard Cohen, 77, is No 2 in the album charts.
"A lot of these people came from the revolutionary postwar youth culture," says Andrew Male, deputy editor of Mojo magazine, which has Cohen on its latest cover. Though this generation has dominated culture since the 1950s, they were not always allowed to grow old gracefully. "They had a crisis in their 30s and 40s, the punks laid into them and then in the 80s they were forced to put syn-drums on their records."
Now, he says, older musicians have sympathetic collaborators like producer Rick Rubin, who gave Johnny Cash and Neil Diamond a raw, classic sound, and are revered rather than disdained as dinosaurs. "If you go down to Cafe Oto in Dalston, all the trendy young people there are checking out Evan Parker, a jazz guy in his late 60s. People are seeking authenticity – people who have a story to tell."
He adds that downloading and iPod culture mean that people now listen to new and old artists. "People buying music are ferally into the latest mixtape, but they're not excluding musicians in their 60s, 70s and even 80s. The punk idea of 'clear off, grandad' doesn't exist any more."
Yet do artists really improve with age? Comic Jackie Mason, 75, who has just started a season in the West End, believes so. "The more the comedian knows, the better he gets. As long as you put the hard work in, you'll inevitably improve with time and experience."
"Lucian had painted every day for over 70 years," points out Gayford. "He'd spent longer than anybody in art history trying to paint flesh and human skin and life in oil paint day after day so it was a tremendous depth of experience and observation he'd accumulated. If you maintain your energy and ambition and desire to create a new painting tomorrow, you get better."
Author Diana Athill, 94, who won a Costa award for her memoir three years ago, says sustaining an artistic career in old age "depends entirely on genes and health. If you're healthy and you have the genes that make you creative, they go on working for quite a long time."
However, she says, "people do taper off. The later novels of many people who write lots of novels are less good than their early novels."
It's a subject tackled in an essay by the novelist John Barth, now 81, in the literary magazine Granta, in which he says that he believes the well of his inspiration has run dry. It's an attitude that cuts little ice with novelist Edmund White, 72.
"I've known Barth all my life," he says. "He's very at ease financially and always sits at the same three desks. He should get rid of desks and write in a train and give away all his money. Then he'd be forced to write for money the way the rest of us do and he'd find inspiration right away."
White says that after mining his own life in memoir and fiction, he has tried hard to find new things to write about. His new book, Jack Holmes and his Friend, is about a friendship between a straight man and a gay one. "It's a subject you see everywhere around you in urban life, but I don't think has been written about at all, or very little."
Gayford says Hockney and Freud's longevity was partly down to their willingness to change direction. He says that when Hockney found his new subject matter after leaving Los Angeles, the countryside around his home in Bridlington, East Yorkshire: "He told me he thought he had more energy now than he had 10 years ago. His huge new studio and the prospect of having these grand rooms at the Royal Academy acted as a tremendous energiser."
Hockney has also asserted his relevance to the modern era by making work on iPads and iPhones. "Artists have that in their favour, which writers don't," says White. "They can constantly use new techniques to refresh themselves."
"I think Hockney's spendid," says Athill. "The way he absolutely grabs at modern technology – most people of his age do shy off it so I think he's almost unique in that."
Old age is also a subject matter. Though White claims that "people don't want to read books about old people", Cohen's album is called Old Ideas, Allen has made films about his mortality since his 30s, and Freud, according to Gayford, "regarded ageing as a picture opportunity. I imagine he took Rembrandt's and Titian's late self-portraits as an example and painted some very unsparing pictures of himself in old age.
"He said to me on more than one occasion that one of the greatest disadvantages a painter could have was fear of death as it would prevent you from exploring properly the mortality which is built into painting human beings."
These artists, of course, have had the benefit of long, productive lives: Ono's husband John Lennon was murdered aged 40. She believes that he would, like his peers, be "making music, doing some drawings, he might want to make a film. He would be jumping on the computer because we didn't have that. He was always interested in new stuff – with computers you can communicate with the whole world at the same time, you can make digital art. I'm sure he would have loved it."
Ono believes that working keeps artists alive: "Da Vinci was always good, but in his late years he did something incredible. Picasso was like that too. Older artists, when they felt they made their message and could go, they went very fast, but some artists don't feel that they have done enough and they keep on living."
Though she puts it in less mystical terms, Athill agrees that artists should avoid retirement: "They should continue as long as they possibly can, just for their own sake. Maybe what they're producing is not so entertaining for other people but it keeps them happy."
