When did age become the forefront of fashion?

I'm starting to utter, "I simply don't have a thing to wear", every time I slide open my wardrobe door, and now I know why. Having spent two days scrutinising catwalk photos from the spring/summer 2009 collections, along with images of the fash pack - and Brat fash pack - I can confirm age is now the great fashion divider. Consider yourself "past it" if you are over 28. When is this obsession with youth ever going to end?

How sad the only female shortlisted on the Man Booker Prize, Britain's pre-eminent book award, Linda Grant, 57, revealed this week she is more anxious about choosing an "appropriate" dress for the awards ceremony than actually winning. But I know what she means. For 2009, once again catwalk fashions appear to be aimed solely at the sulky, snarling teenagers and twenty-somethings - former models, socialites and actresses - who perched menacingly front row for all to see.

Up on the runways, meanwhile, the army of skinnier, younger models united by gloomy faces and platforms stomped along wearing clothes mostly off limits to anyone born before 1988. Of course, all this doesn't remotely affect fashion editors, who are, remember, looking at trends for fantastical shoots in their magazine spreads. Bring on the trends, they shriek. The more, the madder, the merrier! But on a more serious note, it's no wonder these catwalk shows are reported to have given many buyers - already shivering in the chilly economic climate - the jitters. Looking your age (unless it's 16) is something to strike fear into the hearts of all women, even the most stylish.

You'd have thought fashion designers would have come up with a Botox solution for clothes by now. Ones that would make us look younger and smooth out the wrinkles and muffin tops, rather than do minis (Dior), bra tops (Prada), rise and fall hemlines (Nina Ricci) and strapless, backless, sideless (everyone) bits which can and will make anyone over 30 look even older. When did age, which we'd all prefer to forget about, suddenly leap into the forefront of fashion? Meanwhile, who is writing the rules about when you can start or stop wearing skin tight leather leggings, false eyelashes and giant platforms?

The only thing worse than seeing those girls who seem to have nothing else to do besides go to fashion shows - Zoe Kravitz, Clemence Poesy, Alexa Chung, or Emma Watson - working that teensy skirt, Pre-Raphaelite hair, just-pulled-it-together scruffy look over and over again is seeing L'Wren Scott, Jemima Khan and Stephanie Seymour trying desperately to look younger than they really are. Shoehorning themselves into a combination of skin tight leather leggings, sheer tops and teetering platforms gave the mutton metre the largest trilling since Gwyneth wore those skyscraper heels with bare legs.

But what's the alternative? Do a Carla Bruni Sarkozy/Sarah Palin, and pull on a pencil skirt suit and wear your hair in an up-do, loosely translated as, "I'm a grown-up"? Certainly don't wear any designer gear unless you want to look 100. Madonna may not like to hear this but it's become uncool to be, (whisper it) 30, let alone 50. And yet most successful designers, editors, buyers and shoppers are.

Wouldn't it be nice if designers such as Giles Deacon, Alexander McQueen and John Galliano, who claim to love "older" women, showed it? And while you're at it, guys, stop inviting kids to fashion shows who are more interested in their Blackberrys than designer gear. On a positive note, amid all this market chaos, the first ready to wear fashion line from the maternity giant Isabella Oliver was launched in East London this week, a sort of Donna Karan-meets-Stella McCartney range for the post Sex and the City generation. Coming from the former designer of Victoria's Secret and marketing director of Orange, I suspect they are on to a good thing, addressing a gap that has been overlooked for far too long.

Until the catwalk mirrors genuine demographics, we can look forward to It bags, statement necklaces and bootees (yawn) dominating fashion ? again. Women might look stupid, but we are not daft. Designers beware - next summer could be a case of not so much "I don't have a thing to wear" as ? "I'm not wearing THAT".