This a phrase they use to apply to ladies of a certain age who were out on the town looking for men, or dressing to attract the opposite sex in a younger style. This was before terms such as MILF and cougar. Invariably, they were divorcees and like Coward's Mrs Wentworth-Brewster were looking for something on offer so much bigger than old papa, a rather macabre spectacle indeed. The last time I heard it used often was back in the 80s. The male equivalent was "The oldest swinger in town", again a phrase not heard anymore. Well, in today's Telegraph, Hugh Francis Anderson has decided to ressurect "Mutton dressed as lamb....", but now for metrosexual males like Beckham who refuse to grow into a more refined and dignified old age, a rather confused piece of journalise and guide on the sartorial art of dressing in midde age for men who clearly haven't got a clue:

Style, it appears, is nothing short of a mystery. Just when you think you know where you stand, it goes and pulls the Persian rug from right under your suited and booted legs.

Take this week's example of David Beckham. Normally, we're on a sure footing with Becks: you know that this is a man who dresses well. It's what twenty years in the limelight and a fashion designer wife get you. Beckham wears clothes that are at once trendy and timeless; cool and classy. Follow his lead and you can't go wrong.

Or can you? A recent photo posted to the picture sharing website Instagram showed Becks Snr, 40, wearing disturbingly similar clothes to his son Brooklyn, 16.

It's not the first time David has been shown up by his photographer/model son. Only last week the duo were photographed walking the streets of New York looking like a pair of lads (with three decades between them).

Sorry David, but the term 'mutton dressed as ram' springs to mind. When your son starts to wear the same clothes as you (or vice versa), you should know it's time to retire the knee-length sweat pants for something a little more, well, middle-aged.

As the poster boy of metrosexuality – a 90s trend that taught men to look in the mirror and start taking care of their appearance – Becks Snr is representative of his generation's mid-life struggles. How do you carry an unashamedly vain mindset into your middle ages, when your skin might not be so clear, your tummy so toned, and when the new wave of twentysomethings  look a lot better than you do?

Who else struggles to answer this question? Russell Brand indisputably, Noel Gallagher arguably, and Pete Doherty probably (he still styles himself as a shabby Victorian chimney sweep with a side of morning after – but at the age of 36, perhaps we can let the troubled frontman off this particular charge).

Other metrosexual men have bridged the generational divide more elegantly: we can all learn lessons from Brad Pitt, Pharrell, even Johnny Depp. But if you're going to cross the age gap, you've got to do it right way.

‘How?’ I hear you scream. Well, for a start, a man in his 40’s should never dress like a GCSE student, however trendy the clothes may be. Use that as your guiding principle and the following pieces of style advice as general rules to stroll through your golden years with grace, dignity, and unperturbed style.

1. Fit for Form

Wear clothes that fit correctly. It's a notion that is easy in principle but painfully hard to execute in practice.

OK, so the ‘kids’ may don the capricious extra-long T-shirt, skinny jeans and oversized shell jacket, but the earth-shattering combination of so many varying sizes can make the older man look as if he’s been plucked from the Moroccan hinterland, rather than the streets of Shoreditch.

Getting the basics is key. T-shirts can look great but only if they are neutral in colour and not body hugging. Unless you’re lucky enough to have Becks’ body, you need a little room for the obvious protrusions.

Similarly, neither skinny nor boot-cut trousers will do. The most flattering, universal and timeless trouser-cut is the slim-fit. They not only offer shape and structure, but are also ergonomic enough to never broach the sticky subject of a fashion faux-pas.

2. Master the McQueen

We all know Steve McQueen as the ‘King of Cool,’ and there’s a reason for this: the way he dressed. McQueen embraced simplicity and oozed style, so if you want to grow old with grace, simply replicate any of his classic outfits.

Polo necks? Yes. Trench coats? Yes. Knitwear? Hell yes. Layer lightly, neutrally and finish off with a vintage motorcycle (if you have one). No scooters allowed.

3. Run for the Hills

Trainers are the bane of men’s style. Yes, they have risen, with remarkable pace, to valiantly sit at the head of the men’s footwear table, but they are simply not a suitable choice for the older man (unless you’re Keith Richards, in which case  you can do what you like).

These are your finest years, so treat them with respect. Loafer, Oxford, Derby, Monkstrap, Chelsea – all timeless styles to add to your wardrobe repertoire. So what if Becks wears trainers? We’ve been conditioned to appreciate how stylists dress him; but we can’t say the same for you.

4. Tinker Tailor Style Spy

There’s never been a more appropriate time than your fifth decade to invest in quality tailoring. In fact, your greatest style weapon is that of a tailored suit. Yes, it will cost; no, you shouldn't quibble as it will make you look so much better.

Again, simplicity is key. Choose single over double-breasted, add a waistcoat if your torso needs flattery, and make Savile Row your destination of choice – Gieves & Hawkes, Hardy Amies, Kilgour and Richard Anderson are the tailors for the mature.

Think George Clooney not Gary Busey.

5. Simplify to Accessorise

It’s great to add a touch of pizzazz to your outfit, just don’t go too far.

Look at Bill Nighy for example – a silk scarf, simple pocket square and a fine timepiece. That’s all you need. Err on the side of caution here; avoid excessive jewellery and overtly flamboyant colours. The key is to look stylish, and style is always timeless.

6. Originality is key

In everything we see, and therefore everything we do, we are being robbed of our originality. So and so wore this, such and who wore that. Forget it and stick to your guns.

Going back to that double-vision picture of the camouflaged Beckhams, perhaps David would have got away with it had he not called into question his mutton dressed as ram status in the pic caption. "Not sure if I'm a cool dad or Brooklyn is thinking seriously we have similar coats on dad," wrote the former footballer.

The key to any outfit is confidence. If you happen to love claret coloured corduroy shirts then layer them up, accessorise meticulously, and head out with your head held high.