There is something rather exhausting about being a woman in midlife.

Your weight. BMI. Waist measurement. Blood sugar. Cholesterol. Steps. Calories. And now, apparently, biological age.

My first reaction was: Oh, brilliant. Another thing I can fail at.

To be fair, I had half expected the machine to tell me I was about 100.

What appeared on the screen was considerably more reassuring. Boditrax gave me figures for things such as muscle percentage and body composition, and although I knew they were estimates rather than some infallible medical verdict, something interesting started happening.

Month after month, I began to recognise patterns.

When I exercised regularly, the numbers changed. When I changed the kind of exercise I was doing, they changed again. Most noticeably, when I started doing more strength training, my muscle percentage began to increase.

I loved it.

There was an instant little dopamine hit in seeing evidence that something I was doing might actually be working. Obviously, I was rather less enthusiastic about getting on the machine during the months when my diet had gone spectacularly off piste and I suspected the numbers might not tell me quite what I wanted to hear. Apparently, my enthusiasm for health data has limits.

But one number stubbornly refused to play along: my BMI.

It barely shifted. My weight was not dropping as I became stronger. Sometimes it went up. Yet other measurements were moving in what looked like a positive direction.

And that was when I started wondering what these numbers were actually telling me. If my weight could increase while my muscle percentage increased, and a machine could give me a “biological age” on top of all of that, which number was I supposed to believe?

More importantly, why did I care quite so much?

Women have spent decades being told that our bodies are projects. Lose this, tighten that. Eat less. Move more. Look younger. Just … try harder.

Then we reach midlife and discover that the rules have changed again. Hormones shift. Muscle matters more. Sleep can become spectacularly unreliable and recovery takes longer.

The body we had at 30 is not necessarily the body we have at 50. That does not mean we are doing something wrong.

Chronological age is straightforward. It is simply the number of birthdays you have had.

Biological age is much less tidy. It is a broad way of estimating how your body appears to be functioning as it ages.

There is no single standard clinical test for it. Different tools estimate biological age in different ways, using measures such as fitness, body composition, metabolic health and blood markers. Research methods may also use biological markers such as DNA methylation.

An estimate can therefore come out higher or lower than your chronological age. Interesting? Certainly. A definitive verdict on how well you are ageing? Not quite.

That distinction matters to me, because I had already seen how quickly a number could start directing my behaviour. If biological age becomes yet another score that makes women panic about whether they are ageing “correctly”, we have simply invented another way to make ourselves miserable.

The latest NHS England data makes for uncomfortable reading. Around two-thirds of adults in England are either overweight or living with obesity, while 70% have a waist-to-height ratio above the recommended level.

That does not make BMI useless. It means we need to understand what it can, and cannot, tell us.

BMI is a simple screening measure based on height and weight. It does not directly measure body composition, fat distribution, fitness or metabolic health. Two people can have the same BMI and very different health profiles.

I haven’t always thought about weight this way.

When I worked at The Journal, a group of us used to walk to Newcastle’s Grainger Market on our lunch break for weigh day. Once a week, we would pay 20p, step onto the scales and receive a little ticket with our weight printed on it.

That was it. No muscle percentage. No body composition. No strength, fitness or metabolic health. Just one number.

I used to staple those little tickets into my diary so I could track my progress. At first, it probably felt quite harmless. Then the number started acquiring far more power than a 20p ticket had any business possessing.

I stopped eating lunch because I was frightened it might make me heavier. On weigh day, I thought about what I was wearing. I chose lighter clothes. I took off a layer before stepping onto the scales.

All to make one number slightly smaller.

Looking back, I can see how wrong that was. I wasn’t measuring my health. I was organising my behaviour around a weigh-in.

And I suspect this is why biological age bothered me enough to start researching it.

Women have been given numbers to chase for years. Weight. Dress size. BMI. Waist measurement. Calories. Steps. Now we can add metabolic age and biological age to the collection.

The technology may have become considerably more sophisticated since my 20p weigh-ins at the Grainger Market. The uncomfortable question is whether our relationship with the numbers has.

Nor can BMI tell me how I feel climbing the stairs, carrying the shopping or trying to keep up with Cyrus in the park. Those things matter too, particularly as we get older.

If there is one thing I wish more women heard during their forties and fifties, it is this:

Muscle supports strength, mobility and physical function, and maintaining it becomes increasingly important as we age.

This is one reason I have become rather fond of the gym. I do not go because I believe every workout should punish me for what I ate. I go because I like feeling strong.

There is something deeply satisfying about discovering that an exercise which once felt difficult has become manageable.

It is not glamorous. Nobody needs photographic evidence of me lifting weights. But I notice the difference in everyday life, and that feels far more useful than whether I can squeeze into the jeans I wore in 2007.

Movement matters, but it does not have to mean an hour in the gym followed by a smug green smoothie. A workout is useful, but so is the movement that happens between workouts: walking, taking the stairs, getting up from a desk or dancing in the kitchen with Cyrus.

The important thing is finding something we can sustain around work, family, hormones, tiredness and the general admin burden of being alive.

Midlife women do not need another health plan that requires us to become entirely different people.

Blood sugar regulation is another part of the wider metabolic-health picture.

Some research has linked poorer glucose regulation with biological ageing markers, although that certainly does not mean a single blood-sugar reading can tell you how old your body is.

The practical lesson is considerably less dramatic: eat in a way that supports your health, move regularly, maintain muscle and pay attention to what is happening in your body.

In other words, the advice is remarkably boring. Which is probably why it works.

There is no magic ingredient hiding at the back of the kitchen cupboard.

And then there is sleep. Ah, sleep. The thing we all know we need and the thing our bodies sometimes seem determined not to provide.

When I am exhausted, everything feels harder. Cooking something decent feels harder. Exercise feels harder. Resisting that fourth coffee in the gym with friends definitely feels harder.

And in midlife, when hormonal changes can make sleep less predictable, perhaps sleep needs to graduate from the category of irritating wellness advice and be treated for what it is:

Perhaps the question we should ask is not:

Perhaps it is:

That feels much more useful to me.

I want to be strong enough to carry my shopping, fit enough to dance, healthy enough to keep up with Cyrus when he’s running in the park and energised enough to enjoy my life.

And, perhaps most importantly, mentally well enough to stop treating every wobble as a personal failure.

Looking after our health matters. So does paying attention to strength, sleep, movement and metabolic health. But there is a difference between caring for your body and spending your life trying to correct it.

Maybe ageing well is not about making the number smaller. Maybe it is about making the life bigger.

Frankly, that is a biological clock I am much more interested in.

Instead of asking whether your body is “young enough”, try asking: