Edmund White once said that his life was a field trip. Whatever happened, whoever he loved, all of it was material for his novels. He would look at this life and think: “My writing will turn all this evil into flowers.”

But when I call the American novelist and memoirist at the house in Florida where he’s staying for a couple of weeks, he tells me that his new novel, Our Young Man, is an exception to the usual rule. His celebrated trilogy of novels A Boy's Own Story, The Beautiful Room Is Empty and The Farewell Symphony is essentially the story of White’s life from boyhood to middle age, but Our Young Man, he says, is a pure work of imagination. “I guess it’s what novelists have always done,” he says. “But it’s sort of new to me.”

Is a pure work of imagination possible though? On the face of it, Our Young Man has nothing to do with White: it’s the story of a French male model who moves to New York in search of work in the 1980s, but the traces of the novelist’s life are there all the same, intertwined with his elegant, perfect sentences: the shock and excitement of going to live in another country, the effects of Aids on the gay community, the changing face of gay rights, and, above all, the slow effects of ageing.

The main character in the book, Guy, is in his late thirties when we meet him and is managing to defy the marks of age, but only just. At one point he looks in the mirror and realises that his jawline will be the first to go: it is a dam waiting to burst.

As for White, he is 76 and the effects are slow but sure: he has to take 55 million medicines, he says, and walks with a cane. His speech is also a little slower and he is still managing his HIV positive status and the after-effects of a heart attack. He is, he says, semi-well.

He also says he is pretty sanguine about it all, although just like Guy in the novel, he was not always so relaxed about ageing. At one point, Guy thinks to himself “I’m young and handsome but I won’t be always” and White remembers a similar thought occurring to him 50 years ago as he was walking along the seafront in Florida.

“I was never very perfect I’m afraid,” he says, “but when I was 22 I remember being on the beach and everybody was looking at me and I was in a white swim suit and I thought I’ll never look this good again and I never did. But I never gloried in that – I hated it and found it oppressive.” And then he laughs. “I guess I’m more the hunter than the hunted.”

In writing a novel about youthful beauty and one man’s efforts to maintain it, White is aware of the parallels with The Picture of Dorian Gray – indeed, he is a great fan of Wilde’s novel and wrote an introduction to the Oxford edition – although he says his character is quite different. Gray is evil and hurts and kills people and is unbearably flippant whereas Guy is slightly dimmer and much nicer; Gray causes pain deliberately; with Guy, it is accidental.

Guy is also surprisingly likeable, even though he shouldn’t be. He’s good looking, he has lots of money and lots of lovers and at the beginning of the novel has moved to New York and is having a wonderful time. The only downside is that, after Paris, he finds New York a little dowdy and provincial, which is where another of the traces of real life comes in as White also did the transatlantic move, albeit the other way round from New York to Paris.

White relocated in 1983 and, like Guy, was struck by the huge cultural differences, which he says still exist today. The British and French, on the whole, he says, value self-abnegation whereas the Americans value self-advancement, which is why a braggart like Donald Trump can do well. In the novel, Guy complains that the Americans are crude and I ask White if he thinks it’s the crude and unsophisticated type of American that explains Trump.

“I think he’s a TV star, that’s part of it, and people are familiar with him. I think he also breaks all the taboos which people find exciting and funny even. And the obvious thing people say is that he’s a Washington outsider, but the American public has been fed this nonsense for years that nothing that comes out of Washington is good whereas actually we’ve made enormous progress in all kinds of domains in the last 20 years – maybe not economically, but socially we have.” As for a President Trump, that would be a disaster, says White, especially in foreign affairs and he sums the man up with a sentence he might have been working on for weeks but hasn’t: “He’s unbearably rude and tragically spontaneous.”

However, White would like to point out that not even Donald Trump can put him off America. After his 16-year sojourn in Paris, White is back living in New York. I point out that it will be book number 30 or thereabouts and ask him how he gets through them all. “Partly, it’s poverty – I’m always waiting for the next payment.” Hasn’t writing made him wealthy? “I think I have about $40 in the bank. But I have lots of leisure and that’s fun.”

He has clearly had quite a lot of fun with Our Young Man, which is full of White’s tropes: beautiful young men, lustful older men, and lots of exuberant and inventive sex, all written with engaging openness. He also returns to the subject of Aids and points out how much has changed for sufferers since the 80s when the novel is set. By the end of the book, Guy’s lover Fred is dying of the disease and there is a power struggle at the side of the bed between Fred’s lover and his two horrible sons, who want to do Guy out of his inheritance. Guy says, “The family almost always wins, no matter how shitty they were to their relative.” Now it’s changed.

“With gay marriage, definitely,” says White. “It elevates the partner to being a husband. In my own case, it’s made lots of differences because I’m married to my partner and when I had my heart attack, it was considered perfectly normal for him to come every day to the hospital and discuss my treatment and so on, whereas in the past relatives might have swooped in and kept him out altogether.”

Interestingly, White says he was initially opposed to gay marriage even though he was present at the Stonewall riots that started the gay rights movement and, as one of the first gay writers to explore his sexuality explicitly, arguably helped “normalise” gay life. In his bohemian world, he says, marriage was ridiculous, unnecessary and an ugly symbol of how the straight world worked. He came around when he realised gay marriage would annoy the religious right. Could there be a better reason for doing it?

White’s next project is a book about books, a memoir about his life as a reader, which means it’s back to more familiar Edmund White territory: books as a record of the field trip of his life. He’s writing it just now, in his friend’s house in Florida, although he says he is taking it relatively easy. There are no early mornings or late nights. For the moment at least, the field trip of life is happening somewhere else.

Our Young Man is published by Bloomsbury, £18.99