Cindy Crawford, pictured, and Demi Moore have 'forever faces' (though Cindy has had the grace to admit that she owes the quality of her skin to her cosmetic surgeon).

We used to know what forty-something looked like. It meant short, neat hair, sensible clothes and the onset of middle-age spread.

It meant less focus on yourself and more on those around you (who’s going to be looking at you, anyway?), a time for slipping gradually into the cosy cardie of your middle years. “Forty, fat and frumpy” was the tag that women dreaded, not least because it was so often true.

Now, forty-something looks… different; none of the old rules seems to apply. Thanks to those Desperate Housewives, we’ve come to feel that tousled tresses aren’t just for youngsters.

Forty-something mothers borrow their teenage daughters’ skinny jeans, chunky ankle boots and jackets – they’re trim enough after all that pilates. And no one bats an eyelid, not when their lithe-limbed, 40-plus role models Liz Hurley and Elle Macpherson are flaunting their just-as-perfect-as-ever bodies.

Botox and wrinkle-fillers, skin peels and SmartLipo – procedures that hadn’t been invented a generation ago – are becoming the norm, to the extent that many women in their 40s appear peculiarly ageless.

Cindy Crawford and Demi Moore have “forever faces” (though Cindy has had the grace to admit that she owes the quality of her skin to her cosmetic surgeon).

And while “45-year-old mother of three”, is still a loaded description, when you see it alongside a photo of Yasmin le Bon and her teenage daughters, you realise the big 4-0 is no longer such a major stepping stone towards old age.

“Forty is just a little step,” says Dr Nick Lowe, consultant dermatologist at the Cranley Clinic in London.

“If a woman comes to me in her 30s and takes my advice on looking after her skin, I can certainly keep her looking that way until her early 50s.”

That advice will include trying out non-invasive and non-surgical treatments; lasers and radio-frequency devices, as well as Botox and fillers, along with broad-spectrum sunscreen by day and prescription skin-repair creams by night.

The stigma of messing around with your face has vanished. This has been aided by the plethora of extreme makeover TV shows and an increasing desire among women with well-known and well-preserved faces to confess to having work done.

“If they say it’s all down to yoga and face cream, they’ve normally done Botox and fillers,” said one industry source. “If they’re admitting to Botox, there’s usually been an awful lot more than that going on.”

It’s become hard to gauge how old women actually are. Celebrity nail technician Andrea Fulerton sees many famous faces close up.

“Women are looking after themselves so much better nowadays that they always look at least five years younger than they are and that goes for their hands, which used to be a real giveaway of age, as well as their faces,” she says.

But cosmetic work is a slippery slope. At first it’s just powder and paint – the clever use of the latest hi-tech cosmetics.

Next, there’s eyebrow-shaping, hair-dyeing and facials, possibly involving machines with electrical currents to liven up slackening muscles. So far, so acceptable. But then come needles delivering line-relaxing Botox or fillers that plump up shrinking lips, puff out cheeks or pad out hollows. It sounds scary. It is scary, but it’s a transition that is becoming a lot easier to make. In the future, it will be easier still as the lines begin to blur between the treatment options.

Face creams will become more powerful and personalised. Already you can have a cream tailored to match your precise skincare requirements. Bionova is a cult brand available at Harrods that prompts biologically active substances within the skin to trigger self-healing processes.

Then there are the prescription anti-ageing creams containing tretinoin, a derivative of vitamin A, which so far has been the only thing clinically proven to reduce wrinkles. These creams will be prescribed more often as wised-up consumers demand them.

Technically, face creams are cosmetics, so should not make a physiological change to the skin. But there are two on the market (Olay’s Pro-X, available only in the US at present, and No 7’s Protect & Perfect Intense) that have been shown by stringent clinical tests to rejuvenate wrinkled skin in a way that could previously be achieved only by the prescription--only treatment tretinoin.

Pro-X, just like L’Oreal’s Youth Code, uses technology based on genomics – working out what has changed, in terms of the genes between young skin and old skin, then identifying ingredients to tackle those changes. Its potential is mind-boggling – once scientists have worked out which genes they need to tackle, they can find ways to activate the right “youth” genes to, say, produce more collagen or reduce inflammation within the skin.

The menu of non-surgical treatments will expand as new technology develops too. There will be machines that can use combined laser technology to tackle pigmentation and resurface skin at the same time. And face and body sculpting using stem cell-enhanced fat grafting will become more widespread.

We will even be able to pop pills to return our hair to the colour of its youth. L’Oreal has been working on hair re-pigmentation technology for years and hopes to have the results on sale within a decade.

Another major reason why women are looking younger at 40 is a shift in our attitudes to ageing. Or perhaps that should be to growing up. There used to be a divide between the generations because women of a certain age surrendered to it.

Now, the middle-aged want to stay young, act young, think young. They gather friends on Facebook; they tweet. Along with their teenage daughters, they are addicted to Grazia and pore over the weekly charts of top new looks.

Better health and healthy habits are another contributing factor. Pilates, FitFlops and low GI are the staples of the “are-you-really-40?” generation. They get their five-a-day, 10 000 steps and eight hours of beauty sleep.

So how will 40 look in 40 years’ time? If you can afford the work, and attitudes towards it continue to become more permissive, then, unless you insist on ageing gracefully, why not?

And in the future, if you can’t afford any work, it’s going to show, in the way that today in the US the poor are marked out by their bad teeth. Barring a volte-face, the pressure for women to look young for their age will increase.

Young girls today use sunscreen daily, avoid sunbeds and have never smoked. They’re savvy about popping pills – high-dose fish oils and antioxidants – to maximise their skin health. They started on pre-emptive Botox and vitamin A creams in their early 20s.

They don’t lie on the beach and by the time they’re 40, they’ll be laughing. – Daily Mail