Novelists are not lion tamers. Just because they are old and still doing their job does not automatically mean that they are good at it. The trajectory for most literary geniuses is down. Where else is there to go? After all, writers are people too, and when people get old they get, well, soft.

They no longer seek to change the world. Their furies and passions no longer spit and fizzle and force themselves out in explosive ways, because after 50 years of living (or 20 for our shorter-lived literary forbears), the wonders of life have mellowed.

It's not that old people write only about pipes and slippers — all too often they write about sex, death and all the extreme situations between. But there's no getting away from it — it's so far from being fresh as to be yukky. And I'm not only talking about certain old white Americans who famously enjoy writing about wrinkly old boys getting it on with nubile youngsters. When Alice Sebold had Helen, the middle-aged protagonist of her latest novel, hook up with her friend's teenage son in the back of a car, she was joining the ranks of older authors frenziedly asking themselves if they've still got it.

Not that ageing can't be a wonderful subject. But it is not what literature is about. Literature is about change. Revolution, revelation, challenge and unrest. It is about forcing us to do things differently. About making things new and seeing them for the first time. This is what every generation must do, in every walk of life, but writing is (and always has been, since Chaucer, since Sophocles) the crucible in which our future selves are formed.

The Romantics are the most obvious example. They started young, they struck while the iron was hot, and even when marriage and children came along (earlier then than now), they didn't — more's the pity for their wives — let it stand in the way of charging around Europe in pursuit of the muse. This means you, Samuel Taylor Coleridge (another example of a writer gong to pot — well, laudanum — in his unproductive dotage). In 1819, Keats wrote La Belle Dame Sans Merci, The Eve of St Agnes, Bright Star, Lamia and his Odes. He was 24. Had he been 84, he'd have been in bed long before the stars came out; he'd have strained to hear the skylark; he'd have dropped the Grecian Urn. And with a bit of luck he'd have forgotten where he put Chapman's Homer, and spared us his tired lines on the 247th time he had look'd into it. That goes for the whole fell-walking, canal-swimming, college-green burning lot of them.

And it's not because they knew death was coming — their octogenarian selves would know that better — it's because they were changing every day and every day the changing world revealed itself anew. It's hormones. Love, food, sex (or “women, wine and snuff”, in Keats's case), nature, politics, art. These things can be enough to make you cry, kill and, crucially, write, when you're only a few years into adulthood.

Today's young romantics — those writers who cause a fuss with their youthful edginess and may or may not be geniuses — are important in the same way. They have fingers in all the hottest pies (race, sex, politics, music, etc) and the guts to leave them there until they burn. But it is not their parents' generation that they are legislating for, it is their own, and that is why is why their parents' generation looks down on them and claims that they get published only because the book trade thinks youth is sexy.

Well, it is. It sells. Crucially, it sells to young people. And if the under-25s are to come to literature and make friends with it — essential if they are to avoid becoming barbarians and making the world worse — we must hook them when they're young. If it takes a pretty, spotty, or shaggy-haired author photo, or the promise of drugs or swearing, so be it. This is what barely-legals such as Richard Milward are for, as the title of his much-vaunted youth-nov, Apples, suggests.

Of course, my wrinkly opponents could claim that writing is a craft and you need the practised skill and learned wisdom of age to do it well. But history disproves this. In the 20th century alone, the list of great authors who published great things before they were 30 is impressive: Greene, Joyce, T. S. Eliot, Woolf, Plath, Nabokov, Salinger and Forster, to name but a few.

And be honest: would you rather read Money or Yellow Dog? The Cement Garden or On Chesil Beach? Look at Updike. Could an old man have created Rabbit? Maybe, but would he want to? He'd be on to bigger, less intimate things. Like terrorists.

The wisdom of an old writer's mind is a fine and private place, but none I think do there embrace. What is art if it is not a celebration of the gut-stirring, eye-popping, pulse-quickening ecstasy of life? Of not knowing Of knowing that there's a possibility that it will be you — your life — that will change things? Perhaps that's the crux of it. For writers over a certain age, the end is written for them, and like rabbits in the headlights, they can't move forwards. So, Lyrial Ballads (1798) or Ecclesiastical Sketches (1822)? Even Wordsworth would choose the former.

The John Llewellyn Rhys Prize recognises and celebrates the best work of literature (fiction, non-fiction, poetry or drama) by a UK or Commonwealth writer aged 35 or under at the time of publication. The winner of the 65th prize will be announced on November 29. Read about the shortlisted books here .

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