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You would think there was only one decision to make when it comes to swimwear post-50: bikini or one-piece?

That’s certainly the big one, but once you’ve picked a side there are a few other things to be aware of to be sure your swimwear isn’t ageing you.

The Plunge-Front Swimsuit

Kate Moss fell foul of this style last week. It’s not the low cut so much as the ‘glamorous party wear’ vibes that make this feel old – along with chiffon beach robes, picture hats and platform sandals.

Kate Moss, 50, in a black swimsuit in the Mediterranean. It’s not the low cut so much as the ‘glamorous party wear’ vibes that make this feel old

Avoid slashed fronts, gold hardware, a glossy finish, lace-up fronts, a belt and anything that hints at cocktail vibes.

INSTEAD: Keep it sporty and fresh – a broderie trim is flattering and not too girly. Combine that with bold lacquer red and you’re in business (M&S’s broderie trim swimsuit, £26, marksandspencer.com).

The Too-Small Bikini

However fabulous your figure, a well-covered bikini is more elegant and flattering at this age.

The one that works best for those over 50 is sufficiently bottom-covering with plenty of side coverage.

INSTEAD: Try M&S’s high-waisted bikini bottoms with adjustable ruched sides so you can wear them exactly the width that suits you (£16, bottoms; £17, top). Plus they have inbuilt tummy control, too.

The Tankini

The worst offender in the swimwear hierarchy. I can’t think of a good reason for choosing one over a swimsuit. You don’t get the smooth clean line of a costume and, if you are past bikinis, you surely don’t want to risk the top riding up, revealing your tummy.

INSTEAD: Go for a sleek one-piece, the best of which will smooth your silhouette and contain you like a light corset – even without body shaping mesh and lining (a Boden swimwear speciality). There are lots of great Boden one-pieces, but my current favourite is the Minori halter tie in cinnamon (£85, boden.com).

The High-Waisted Bikini

Similar issues to the tankini. You think: ‘I’m damned if I’m giving up a bikini but my stomach isn’t what it was so I’ll just go for some big pants.’

The trouble is the high-waisted bikini covering your tummy button shifts all the focus to your abs. It’s strange but true – you need a flatter torso than for a regular bikini.

INSTEAD: If you go for fold-over bikini bottoms, you can adjust them (£39, boden.com). Wear with the Minori halter tie bikini top (£31.50).

The Ruched Front Look

There’s nothing wrong with these other than that they scream ‘wobbly front disguise’ and younger women would not be seen dead in them.

You may think: ‘What the hell! I do need to disguise my wobbly tummy.’ But there are other ways to do that without simultaneously making you look a bit mumsy.

INSTEAD: Get a strong weave that contains you. Try M&S’s tummy-control textured swimsuit in brown (£36).

The Royal Blue One-Piece

I have one, since I liked the shape and they had sold out in the red, but it only gets worn in emergencies as it turns out a royal blue swimsuit – as opposed to midnight blue – is dowdy. Who knew?

Oddly there is a short list of potentially ageing swimwear colours and they include all the tropical brights and strong pinks, although an ice pink can look nice.

INSTEAD: Choose the colours that are chic and anti-ageing now: black, brown, olive, khaki, red or black and white. John Lewis has a good twist-front swimsuit in khaki (£38.50, johnlewis.com).

The Floral Swimsuit

Florals are the worst offenders but all prints will dial up your age instantly. The busier the colour combinations are, the higher the dial goes.

INSTEAD: Go for a small gingham check or stripes like Saint + Sofia’s bestselling cross-front striped swimsuit (£99, uk.saintandsofia.com).

The Low-Cut Leg

This is the position women often retreat to when they’re anxious about showing too much hip flesh, but not only does the line cut you off so you look shorter legged, it instantly adds a decade to your age.

INSTEAD: Try one of the many excellent eye-tricking options such as the illusion cross-back swimsuit in navy with white leg panels from Chelsea Peers (£65, johnlewis.co.uk). You will look like you’re wearing a high-leg swimsuit but have all the coverage of a regular leg.

Monsoon does a contrast trim one too, in black or blue, also from John Lewis (£49).