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

Just when you think you have made peace with your body, along comes another number to worry about. Your weight, BMI, waist measurement. Your blood sugar, cholesterol, 10,000 steps per day, resting heart rate, those dreaded calories. And now, apparently, biological age.

I have to admit, my first reaction was: Oh, brilliant. Another thing I can fail at. Women have spent decades being told that our bodies are projects. Lose this, tighten that. Eat less, move more to look younger. Just … try harder. Then we reach midlife and discover that the rules have changed again.

Hormones shift and muscle becomes more important. Sleep can become spectacularly unreliable and recovery takes longer. The body we had at 30 is not necessarily the body we have at 50, but that does not mean we are doing something wrong.

Unlike chronological age, which is simply the number of birthdays you have had, biological age is a broader way of thinking about how well your body appears to be functioning as it ages.

It can take into account things such as fitness, muscle mass, waist size, blood sugar, sleep and wider metabolic health. In theory, someone can have a biological age that is higher or lower than their chronological age and the concept is interesting. But I think we need to be careful about what we do with it, because if biological age becomes yet another number that makes women panic about whether they are ageing “correctly”, we have simply invented another way to make ourselves more miserable.

The point should be health, not a gold star for looking younger than you are.

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 mean BMI is useless. It just means we need to understand what it can, and cannot, tell us.

BMI uses height and weight. It does not know whether you spend your evenings lifting weights or sitting on the sofa and it can’t tell the difference between muscle and fat. It tells us very little about how you actually feel when you climb the stairs, carry the shopping or chase your child around the park. Two people can have the same BMI and very different health profiles and that matters particularly as we get older.

Because one of the things I increasingly care about is not simply how much I weigh, but what my body can do.

Can I lift something heavy?

Can I get up from the floor without making the sort of noise my mum’s knees used to make?

Can I walk for an hour?

Can I dance?

Can I carry the shopping?

Can I keep up with Cyrus?

Those things count too.

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

We need to remain strong because 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 a particular satisfaction in discovering that something which once felt difficult is now manageable. It is not glamorous. Nobody needs to take a photograph of me lifting weights, but I notice the difference in everyday life. And that, to me, is a far more useful measure of ageing well than whether I can squeeze into the jeans I wore in 2007.

This is another bit of health advice I can get behind. Movement matters, but movement does not have to mean an hour in the gym followed by a smug green smoothie.

Walking counts.

Taking the stairs instead of the lift counts.

Getting up from your desk counts.

Dancing in the kitchen with Cyrus counts.

A workout is useful, but so is everything we do between workouts.

Physical activity can support cardiovascular fitness, insulin sensitivity, strength and mood. The important thing is finding movement that you can actually sustain. And this is where I think midlife women deserve better advice. We do not need another plan that requires us to become entirely different people. We just need habits that fit around school runs, work, partners, ageing parents, tiredness, hormones, dinner and the general admin burden of being alive.

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

Research using epigenetic measures has linked elevated glucose with markers associated with faster biological ageing, although that does not mean a single blood-sugar reading can tell you how old your body really is.

The practical lesson is much less dramatic.

• Eat a balanced diet.
• Move regularly.
• Maintain muscle.
• Pay attention to your health.

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. Sleep affects appetite, mood, recovery, energy and our ability to make sensible decisions.

When you are exhausted, it is harder to cook the decent meal and harder to exercise. It’s also harder for me to resist that fourth coffee in the gym with friends. In fact, it’s harder to feel remotely enthusiastic about anything. This becomes particularly relevant in midlife, when hormonal changes can make sleep less predictable for many women. So perhaps “sleep more” needs to graduate from the category of irritating advice shouted at us by wellness experts and become what it actually is:

This is the bit I care about most. We have become remarkably good at turning health information into ammunition against ourselves. The scale goes up, a waist measurement changes. My Apple watch tells me I slept badly. And my Boditrax app suddently tells me my biological age is five years older than I expected. Suddenly I am catastrophising during a Zumba session.

Health is not a moral judgement. Being heavier does not make you lazy. Having a larger waist does not make you a failure. Missing a workout does not mean you have “fallen off the wagon”. And getting older is not something we need to apologise for. If thinking about biological age encourages someone to take better care of their cardiovascular health, build muscle, sleep properly and move more, wonderful.

If it leaves us frightened of every meal and checking a number before we have even brushed our teeth, I would suggest we have missed the point rather spectacularly.

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 just energised enough to enjoy my life. And most importantly, mentally well enough to stop treating every wobble as a personal failure.

Of course, looking after our health matters. So does maintaining a healthy weight where appropriate. So does paying attention to metabolic health, strength, sleep and movement. 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. And frankly, that is a biological clock I am much more interested in.

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

• Am I getting stronger?
• Am I moving regularly?
• Am I eating enough nutritious food?
• Am I sleeping as well as I reasonably can?
• Am I looking after my cardiovascular and metabolic health?
• Am I enjoying movement rather than using it as punishment?
• Am I speaking to myself with the same kindness I would offer another woman?

Perhaps the healthiest thing we can do in midlife is stop treating our bodies like troublesome employees who are forever underperforming. They are carrying us through our lives. That deserves a little respect.