How the age of the grown-up is now taking centre stage

That's well grown-up," a friend's teenage son tells me admiringly. I can't quite believe my ears. For the past 10 years, "grown-up" has been a pejorative term - implying washed-up, past it, boring. Everyone was gagging to be wild, carefree and young. But now it's suddenly acceptable - cool, even - to be over 35.

David Cameron and Nick Clegg set the trend, of course, ushering in an age of grown-up politics. Cameron's old-school Eton tie is back and elsewhere the catwalks are full of camel and taupe slacks and sensible sweaters. Bling is definitely out, says fashion writer Lisa Armstrong. "The move towards grown-up clothes isn't a minor detour. It's a new ideology."

This summer, the most interesting festivals are targeted squarely at grown-ups. At Edinburgh, cabaret and variety are giving the Fringe comics a run for their money. Last week's Vintage Festival at Goodwood offered shopping and cocktails instead of being dominated by skinny teenagers in microshorts. There was a refreshing mix of age groups wearing retro fashions from the Forties and Fifties.

The Old Vic has revived Noël Coward's Design for Living, the ultimate grown-up threesome play. "Young people love the free spiritedness of the play - which is about people choosing how to live their lives, and is full of passionate love, gay and straight," says its director, Anthony Page. On screen, forget frat boy movies, John Hamm of Mad Men and Rebecca Hall's new film The Town is the "season's most adult film", according to fashion title W magazine.

So why is "grown-up" the new buzz word? Damian Barr who started the Shoreditch House Literary Salon says: "Most of the people who come here are in their twenties. Yet they have an appetite for engaging with writing that reflects the time they live in. Salons were born in tumultuous times and have returned now as a way of helping us all to have a conversation about who and where we are."

But before we "olds" get too smug, Ed Howker, co-author with Shiv Malik of the new book, Jilted Generation: How Britain Has Bankrupted Its Youth, thinks there's such a trend for grown-up style because few young people nowadays can aspire to it. "Adulthood means a home, a job and maybe a long-term relationship. But try getting those when you still live with your parents and are unemployed. Grown-up is what young people want to be - they just can't afford it."

Damian Barr thinks we're in one of those moments before the culture reinvents itself and young people will be at the helm again. "Yes, life for us is competitive and anxiety-ridden. We now have to play the role of grown-ups ourselves. In a way we've found it easy... a bit like when women entered the workforce during the Second World War. We've seen what grown-ups were claiming to do and we've found we can do it better."

Design for Living is at the Old Vic, The Cut, SE1 from September 3 (0844 871 7628).

To join Shoreditch House Literary Salon, contact mrdlbarr@yahoo.com.

The next Secret Cinema runs from September 3-5 (secretcinema.org).