Half-caught a minute or two of that suave revolutionary Tariq Ali on Desert Island Discs last week. Revolution and Desert Island Discs – I mean no mischief by pointing out the conjunction. The wildest of us must accommodate to society's blandishments at last. We age, we mellow, we want to lie on deserted beaches listening to gramophone records.

It was an allusion to ageing that I caught as I was bending down to tie my shoe laces before leaving the house to meet friends for breakfast. Takes me a little longer than it used to, bending down to tie my laces. Tariq Ali I would guess the same, though he has kept himself well oiled. Had I ever had it in me, back in 1968, to be a revolutionary, I'd have chosen to look and speak like him: sad-eyed, remorselessly articulate, a little weary and contemptuous, with a taste for good overcoats. Except that now I think of it he wore a red raincoat in those days, so I must be dressing him in cashmere retrospectively, perhaps as a gesture of protectiveness towards someone whose views I cannot share but without whom I think English polemical life would be the poorer. A dandy of the barricades he was, whatever his coat. His only mistake the black turtleneck sweater. A touch too Jean-Paul Sartre, I always thought. The uniform of cosseted dissent.

There he was on the radio, anyway – Tariq Ali, I mean, not Jean-Paul Sartre – picking his tunes with that same scrupulousness with which he once picked apart plutocracy, when the question of sometimes travelling business class on aeroplanes arose. He said what needed to be said. That at a certain age you aren't averse to comfort.

Of course you aren't. At a certain age comfort is very nearly all you aren't averse to. An eventuality every intelligent person should anticipate. Here is the difference between a revolutionary and a non-revolutionary: the revolutionary is unprepared for age and the changes it will work to his body and belief systems; the non-revolutionary intuits all the retrogressions, complexities and compromises that lie ahead. It is a question of imagination. Revolutions are powered by the young, and the young – at least those who are consumed by the excitement of being young – have no imagination of age. They see old men, not as themselves as they will one day be – enriched by having been both young and old, the shrewder for having experienced all that happens in between – but as obstacles to their energies and fantasies. And in everything they don't imagine they find the exhilaration of their cause. This is why it is insane to be carried away by the politics of youth. The politics of youth are, by definition, the politics of ignorance.

So what does that say about those of us who were not swept up by the universal ameliorative hysteria of 1968? Was our scepticism bought at the expense of our youth? Were we never young at all?

"Bliss was it in that dawn to be alive, / But to be young was very heaven!" Wordsworth, remembering the French Revolution. The same Wordsworth who was later to be mocked for his conservatism by the next generation of bliss-to-be-alivers. And so the wheel of youth and age turns. You are a revolutionary and then you're not – Hitchens, Mamet, Dostoyevsky. But not me. Because no, if bliss to be alive is how it feels to be a young man swept up in revolution, I wasn't young. Bliss to be alive and in love, yes. Bliss to be alive in the flesh and in the mind, bliss to kiss and be kissed, bliss to feel the sun on your back and to taste the red wine as it trickles down your throat, bliss to be lecturing to a thousand students about Wordsworth and the French Revolution, yes. But bliss to be in an anti-Vietnam war march carrying banners about Northern Ireland and inequities at the Hornsey College of Arts and a thousand supposed related causes, no, not for an hour. Not for a minute. Not for the least division of a second.

A march is a march. Don't look to me to solve the politics of it, but if it's peace you want you can't – can you? – go on a march, given that a march is by its essential nature, never mind its associations, militaristic. It combines and opposes bodies. It is a show of strength. It exults in taking back – which means exercising – power. And it employs the same psychology of fear in weight of numbers and intoxication in unanimity and noise as an army. They spoke of peaceful demonstrations in 1968 and then wondered why they always erupted into violence. Cops' fault. Maybe it was, sometimes. But the energy for conflagration is always there in mass movements. The only truly peaceful man is he who lives and thinks alone, and even he as likely as not turns out to be a homicidal maniac in the end.

I went on one of the big 1968 marches. Not as a soldier but a reporter. I had recently returned from my first job as a lecturer in English literature at Sydney University– my own great dawn – and had been commissioned to write about the London demos for an Australian magazine to which I had occasionally contributed innocuous review articles. When the piece I wrote was published I lost the sympathy of just about all my Australian friends. Vietnam was a closer reality to them. Australians were conscripted and died there. For them my politics, which consisted of not wanting to be on any side that had the Redgraves on it, was irresponsible dilettantism. I still don't speak to most them – my Australian friends I mean, not the Redgraves – though I acknowledge now that they were right. The best of causes are espoused by the worst of people. And if you allow the sanctimoniousness of protesters to sway you, you will never protest about anything.

But I know I'd feel exactly the same again. Wouldn't like the sensation of rapturous unison, wouldn't like the conviction of rectitude etched on a hundred thousand faces, wouldn't share the assumption that there is a great chain of wrong out there linking Iraq, Palestine, Darfur, council taxes, plastic bags, the fifth terminal at Heathrow, poultry farming, God.

Old before my time, you see. Which makes it a little irksome having to hang around waiting for the others to turn up – Hitchens, Mamet, Dostoyevsky and the rest – while they slowly claw their way to the truth that some of us were born knowing. That in the end we will all travel business class if we can.

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