Elizabeth Hurley is such a joy. Announcing her 58th birthday with a glorious bikini snapshot from a faraway beach, she looks just as sleek and toned, glam and glossy as she has for nearly 30 years.

But she’s not the only one rocking skimpy swimwear at an age when most women have retreated into a kaftan. Demi Moore has never shied away from bikini pics and looks simply sensational at 60 — and, hey, so do I! There, I’ve said it. The editor made me say it, because look, I’m a bit embarrassed to be held up as some shining example just because my size and shape are the same they have been since my 20s. But I can’t say I don’t enjoy it — or that it doesn’t take a lot of time, energy, and money to maintain.

I didn’t seem unusual in my 30s or 40s, but now I’m 60, people seem shocked that I look the way I do, particularly since I’m not an athlete or a model.

My three adult children have all left home and I run a small, all-consuming online business so I spend most of my day sitting at a desk. ‘So how do you do it?’ people ask.

Elizabeth Hurley says blithely that she moisturises ‘about six times a day’; but I know that looking like this as you shimmy into your seventh decade doesn’t just happen.

Yes, genes help, because there’s not much you can do to change the structural framework of your Body, but there’s a lot you can do with the padding and cladding . . . you absolutely can look like this if you want, but it takes a lot of exercise, constant vigilance over what you eat and drink, plus, in my case, the odd tweakment.

You need dedication and determination to keep it all on track, plus a fair bit of cash — I spend much more on my body than on the clothes I put on it, but I regard it as a long-term health investment.

Lashings of moisturiser won’t go amiss, but that’s the icing on the cake. So, what do I do? Here goes.

When people tell me I’m in good shape, I used to mutter that I was just lucky, until one feisty friend called me out. ‘Excuse me,’ she said. ‘That’s the result of a lifelong exercise habit — own it!’

So yes, I exercise a lot, and always have done, from team sports at school and university, via Jane Fonda videos and step-aerobics classes in the 1980s, to gym work, pilates and all the mad fads I’ve been called to write about for work.

By your 50s, though, you need to take a more thoughtful approach to exercise. Demi Moore and Jennifer Aniston, 54, have both spoken about having to tone down the extreme workouts they did in their 20s.

My back ‘went’, as backs do, when I was 29, and I had to abandon the hardcore classes for pilates that wouldn’t send it into painful spasm.

I limped through my 30s on little formal exercise beyond chasing my small children around, but by my late 40s, feeling stronger, I eased into dynamic yoga — the sort with more jumping about — and more gym work, and stepped this up through my 50s as it dawned on me that it was use-it-or-lose-it time.

We all lose muscle as we age unless we actively work at keeping it, and that means doing strength work —squats, lunges, tricep dips, chest and back moves — with weights. Heavy ones. I don’t love the weights, but I adore my trainer, Zana Morris.

I’ve worked with her on and off for 12 years, and she chivvies me through two online sessions a week (and no, the weights haven’t made me bulky, I’d have to work a lot harder for that). She’s wildly expensive (about £100 a session, zanamorris.com) but I’ve learned that, left to my own devices, I don’t work half so hard. I also do yoga twice a week, usually online (£10 a class), which is a joy, particularly the playful side of it, and helps no end with keeping my ageing frame mobile.

Who knew I’d be able to learn arm balances and backbends, the sort of gymnastics that I could never do at school, at my age?

I dislike cardio, so the most I ever manage is one session a week of six 20-second sprints on the treadmill at the local gym (£56 per month). What with recovery in between each sprint, plus warming up, that takes all of 15 minutes, so while I’m there I often throw in some squats, press-ups and bear-crawls — ‘walking’ on all fours with my bum in the air — which is much easier than doing it at home as I don’t have to constantly change direction so as not to bump into the furniture.

I can’t say it’s easy, because it’s not, but it’s become such a habit, it’s just what I do.

Unless I exercise first thing in the morning, it doesn’t happen, but first thing in the morning, my spine has seized up from lying down all night and it takes ten minutes of flexing and bending it before I can move, let alone work out, with any ease.

Before you start thinking I must hate my body to put it through all this, it’s the opposite. I wasn’t that fond of it when I was younger but now I love it, and am continually amazed by what it can do, from producing three babies, recovering from endless minor back-related disasters and allowing me to exercise like I do as I age, even if my monthly bill for physio, osteopathy and other body work to keep my tiresome back comfortable often reaches £250 a month. Plus Zana, yoga and gym membership.

Why do I put myself through all this? In a nutshell — knowing that it makes a difference, plus a horror of ending up slumped, inert, in an armchair, like the residents of the care home where I used to visit an elderly relative. It doesn’t have to be downhill all the way, and it is never too late to start.

Those aren’t just platitudes or cliches, they’re facts. So much research in the past decade highlights the fact that physical decline really isn’t an inevitable part of ageing.

You have to put in the work — first, by changing your mind to a more positive view of getting older — but you can teach an old dog new tricks.

I feel more confident when I’m physically strong — and I like the way it makes me look, too. If you’re thinking, ‘It’s too late for me,’ I’d urge you to think again. It’s never too late to make worthwhile improvements that mean we’ll continue being able to get out of armchairs unaided and climb stairs with ease.

I’m a big fan of the online programmes offered by GMB Fitness (gmb.io) which cater for all ages and stages of mobility. All you have to do is start at the beginning, do what you can, and keep trying.

I know first-hand that the urge to give up on anything challenging is very real. The trick is to choose, each day, not to give in to it.

Which brings me on to food. In my 20s, I thought I could exercise away the effects of eating and drinking too much, but interviewing personal trainers soon taught me that while exercise will hone and tone your body, your size will depend on how much you eat.

So if you’re larger than you’d like to be, there’s no magic to it: you need to eat less, and in the healthiest way possible. Dieting has become a dirty word, though most women my age will have spent more time than they care to admit on a diet of one sort or another, having swallowed the prevailing cultural view that thinner was better during our formative years.

I was a fat child, first put on a diet by the local doctor at the age of 11 (with the best intentions, that I shouldn’t get picked on for being plump when I moved up to secondary school, as in the early 1970s, being overweight was unusual) and it worked.

However, it gave me hang-ups for decades about what I should and shouldn’t eat, shame around gaining weight and the sure knowledge that while I might appear slim, there is still a fat person inside me.

Believe it or not, every now and then, she makes a break for freedom. I know this sounds mad, given the evidence to the contrary, but every winter, around Christmas, I eat and drink everything in sight because it’s fun, delicious and all part of celebrating with friends and family, and of course my clothes get tighter.

In my own mind, I feel my body is inflating like a balloon, even though I’m 5ft 8in, so an extra 10lb hardly shows under jumpers.

For a month or two, I challenge myself to grow up and be OK with it, because I know people don’t treat me differently when I’m a couple of sizes larger. But come spring I’ve always had enough.

I don’t ‘diet’ as such; I know diets are a waste of energy — I’ve tried most of them, in order to write about them, from F-Plan and Atkins to milk-only (yes really) and all-out fasting; not helpful for someone trying to learn to eat normally. Plus, I know what I should be eating and I bet you do, too: lots of colourful veg and fruit, healthy carbs, good fats and plenty of protein. So, every year, after the Easter chocolate, I cut back on sugar, crisps, refined carbs and alcohol and a few months later, I’m back to normal.

Along with all this, I take a lot of supplements — mostly for what they do for my insides, though many of them have knock-on benefits for my Skin all over my body.

What are they? Collagen supplements and liposomal vitamin C to boost skin strength and hydration. Omega-3, for skin quality and hydration, specialised gut-health pills clinically proven to reduce signs of ageing in the skin. NAD+ booster supplements, to give all of the body’s cells more energy. Magnesium, nature’s tranquilliser. Vitamin D, because we all need vitamin D. High-quality protein powder, to mix into plain yoghurt. And hormone replacement pills. Having oestrogen in your system is magic for skin, hair, joints and maintaining muscle mass as well as quelling hot flushes and brain fog.

The monthly bill for all this? Around £450.

But I’m happy to admit that the willpower for the diet and exercise isn’t quite enough.

I’ve had the odd body tweakment, too, including several rounds of CoolSculpting (from £400 per session), at points where I’ve had more fat on me than I have just now. It’s a technology that freezes fat, causing it to die off and disperse but, unlike liposuction, it’s only suitable for reshaping small areas.

It worked a treat on the pouchy bit of my lower tummy, on my flanks, and inner thighs (and no, I didn’t suffer like Linda Evangelista, whose treatment went wrong).

If your knees or your tummy have gone wrinkly with the years, there’s Profhilo, the hugely popular ‘injectable moisturiser’ treatment which can be jabbed all over the body to act like a layer of long-lasting hydrating serum inside the skin.

A course of treatment (£950) can work wonders for smoothing and tightening crepey skin. I’ve tried it once on my inner arms, and yes, it made the skin there stronger and more taut.

One technology I’m fascinated by is EMSculpt, which sends pulses of high-intensity focused electro-magnetic energy into muscles to make them do the equivalent of 11,000 crunches in half an hour. A course of four treatments last summer (from £2,500) gave my abs a new level of strength.

I’ve just done another course on my obliques (the muscles that contour the sides of the waist) and am waiting to see what that yields.

I have cellulite, but it doesn’t bother me and I don’t believe it bothers anyone else, though I have to say, before this photoshoot, I shot into the French Pharmacy in Marylebone for a session of LPG Endermologie, a form of mechanical massage which banishes fluid retention — and cellulite — temporarily (£130).

The one thing I’d always longed to improve about my body was my tiny breasts, which, after doing a great job of feeding my babies, had shrunk so much they barely filled an AA cup. Sure, they looked great in a mannish jacket, but in other clothes? Not so much.

Around 15 years ago I tried an injectable filler designed for the breasts, billed as an instant boob job, that took you up a cup size —but it went lumpy and didn’t last long, so in the end, ten years ago, I opted for proper implants and I am thrilled with being a B.

That cost around £7,000 but has been totally worth it.

So the next time you see a 60+ celeb looking amazing in a bikini and sigh that it’s easy for some —reassure yourself that it really isn’t. They’re bound to be working hard to look effortlessly good.

I know I am — but I also know that when I saunter into the sea in my tiny two-piece this summer I will be feeling good, too.