A friend and I are debating the critical matter of whether women our age (her: 39, me: 41) can get away with wearing the mini skirts that are currently flooding the shops, as long as they’re ‘teamed’ (I do love a bit of fashion-speak) with opaque tights and big boots.

“No,” insists Izzy, her 10-year-old daughter. “Not even with tights. It’s embarrassing.”

Such rules – especially those dictated by children – make my insides twist uncomfortably. No one tells young people what they can and can’t wear. It’s only once you hit your mid-30s that regulations kick in. “I once saw a really old man in a hoodie,” announces my son.

“Really old?” I ask. “What sort of age exactly?”

“Even older than Dad,” he gloats. “At least 50. The hoodie was black with yellow writing on the front, and the writing said, ‘Yo!’.” The kids honk with laughter.

I’m intrigued now and ask the assembled jury if low-rise jeans are acceptable attire for grown-ups. “Only with long tops,” declares Izzy. “But not pink,” shudders her pal, Ben.

“You’re allowed some fashionable clothes,” Izzy concedes, glimpsing my pained expression, “but not the latest stuff.”

I start to feel rather persecuted. Yesterday, I spent the afternoon with an artist who was wearing vivid red lipstick, a green vest top, a little mini over black leggings, and she looked amazing. She is 58. I’d hedge a bet she doesn’t view certain garments as being out of bounds, or own anything in camel or beige. She seems to have sidestepped the barrage of ‘tips’ on what’s appropriate (the word appropriate crops up frequently, and always gives me a sinking feeling).

Other favoured terms when it comes to 40+ fashion: ‘well-cut’, ‘classic’ and ‘investment dressing’ – all of which make me want to keel over with ennui, and conjure up unsettling images of Margaret Thatcher’s unyielding blue suit and scarily bouffed-up hair, circa 1979.

Where skirts are concerned, a newspaper report informs me “just below the knee is best”. It goes on to explain that ‘scruffy denim’ no longer has a place in one’s wardrobe (I love jeans! My dad wears them constantly, and he’s 71). Yet heaven forbid one should look ‘undignified’. “It’s time to dress like a woman,” the fashion journo tells me.

The most irksome aspect is that, yes, this woman probably has a point. I wouldn’t want to dress like a girl and have small children diving into shop doorways to avoid me. Discovering that you have inavertently been embarrassing, and discussed as such, is pretty horrific. I remember an ex-boyfriend squirming as he suggested I might trim the hair which – unbeknown to me – jutted from a mole on my neck.

“I’ve discussed it with Andrew,” he said – Andrew was his best pal – “and he said I should mention it.” Heaven forbid my mole hair should have been causing offence, and was a matter deemed worthy of – gasp – discussion with Andrew.

It’s easy to become paranoid about such issues, and fear that the entire town is pointing and sniggering behind our backs. As Izzy’s mother points out: “I realised the things I feel most comfortable in – jeans, a black vest top – haven’t changed since I was 19. That worried me.” Black top and jeans? They’re hardly akin to dancing on pub tables in a bra top and polka-dot hotpants. I ask her opinion on the bare-arms issue. “That’s okay,” she says, “as long as you’re wearing a little cardi or shawl on top.” – which, of course, means not being bare-armed at all.

“It’s also embarrassing,” Izzy cuts in, “when adults sing old songs like Chirpy Cheep Cheep.”

“I’ve never sung Chirpy Cheep Cheep!” I protest.

My son then proceeds to reprimand me for using young person’s words – ie, ‘cool’ – even in a temperature context (as in: “I could murder a cool beer”). Nor am I allowed to say ‘wicked’, a word he uses several times a day, and which I have never uttered, apart from when reading stories about witches. “The worst thing,” his mate Ben adds, “is when grown-ups get drunk and shout at the telly.” Izzy, on the other hand, approves of such antics because, she cackles: “They give you money for no reason.”

Money which, I assume, can be spent on lovely, fashionable clothes from which we oldsters are barred. While Izzy approves of my cork-soled sandals, my killjoy son declares they’re “too fancy”. Rather miffed, I ask him what old people should do with the clothes they’re no longer allowed to wear.

“Hand them over to the government,” he says.

The Fish Finger Years by Fiona Gibson is published by Hodder & Stoughton, £6.99. Contact her at hello@fionagibson.com