First we wanted to know how many steps we were taking. Then, we were all about sleep scores, recovery metrics and readiness ratings. Now, we’re after a number that represents something a little more intangible: how quickly we’re ageing. Not the number of candles on our birthday cake, but our biological age – the number that reveals how quickly our bodies are ageing beneath the surface.
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Backed by a global industry that’s projected to exceed $600 billion before long, a new wave of tests and wearable technology promises to tell us something our birth certificate cannot: where we’re at on the timeline in terms of cell, tissue and organ function – and whether or not we can positively influence that trajectory.
The idea that ageing is no longer something that happens to us, but something we can track, optimise and potentially slow is seductive. But is knowing our biological age helping us prepare for the future? Or is it simply another way to make ageing feel like a problem to solve?
Biological age vs chronological age
Chronological age is the easy one: how many years you have lived. Biological age is the more complicated cousin: “It tells me how well your body is carrying those years; a snapshot of how your body has responded to the years you’ve lived,” says longevity lifestyle doctor, Dr Alka Patel.
This is why two people born on exactly the same day might have completely different biological profiles as adults. “A 50-year-old with strong muscle, stable blood sugar, restorative sleep and a resilient cardiovascular system may be ageing differently from someone the same age experiencing muscle loss, poor sleep, chronic stress and metabolic changes,” points out longevity scientist Kayla Barnes-Lentz.
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The nuance? There is no single definitive test. Instead, scientists combine different methods, including epigenetic testing, which examines DNA methylation (the “little tags” our DNA picks up as we age), and blood biomarkers (PhenoAge testing) linked to inflammation, immune function, and metabolic health. Wearables such as Oura and Whoop have also entered the conversation, using measures including resting heart rate, pulse wave velocity and VO₂ max to estimate aspects of cardiovascular age.
However, Barnes-Lentz is utilising newer approaches to explore how other systems, such as the heart, liver and ovaries, age differently, revealing that ageing isn’t a single timeline but a set of distinct biological journeys.
The pros (and cons) of knowing
The appeal of biological age is that it promises something chronological age cannot – a glimpse beneath the surface. Depending on the test, it can provide insights into inflammation, metabolic, cardiovascular, immune and muscle health.
But, as Barnes-Lentz cautions, “the value is not simply in knowing the number; it’s in what you do with it. Seeing a favourable biological age can reinforce healthy behaviours, while a result that feels unexpected may motivate someone to make changes.”
The caveat? A biological age result can also create quite a bit of anxiety, particularly when the number feels out of your control. Barnes-Lentz says one of the biggest limitations of epigenetic testing is that the same sample can produce different results depending on the test used: “The risk is chasing a number that doesn’t tell the whole story.”
How to estimate your biological age
While wearables and testing kits can offer useful insights, Patel says our bodies already reveal plenty about how well they’re ageing throughout the day. She points to three simple measures that need no special equipment: grip strength, walking speed and how easily you can repeatedly stand from a chair.
“Grip strength reflects muscle, nerves, circulation and energy production. Walking speed reveals how effectively the heart, lungs, balance and muscles work together, while a sit-to-stand test offers insight into lower-body strength and power.”
These tests won’t calculate your molecular age, but they reveal something arguably more practical: your physical reserve. “If I walked behind you for a day, I’d probably learn as much about your biological age as your smartwatch,” she concludes.
Does biological age affect women differently?
“Yes, and this is one of the most under-discussed areas of biological ageing,” says Patel.
“While men often follow a steadier ageing trajectory, women can experience a sharper shift during perimenopause (acting as an accelerator), as falling oestrogen affects muscle mass, bone density, metabolism, cardiovascular health, sleep and immunity.”
Crucially, Barnes-Lentz says biological changes may begin signalling this hormonal transition before symptoms become obvious. “This does not mean accelerated ageing is inevitable. It simply means that perimenopause is a powerful window for protecting a woman’s future health.”
What helps to lower biological age
So, what happens if your biological age comes back older than your chronological? Well, like most things, the answer is not to panic. Biological age is influenced by many of the same factors that shape long-term health, and many of them are surprisingly familiar.
Patel calls them the five S’s of slow ageing: sleep, stress, strength, sugar and sociability:
- Sleep is when essential brain, immune and metabolic recovery occurs.
- Stress influences cortisol, glucose, inflammation, immune function and sleep. Short, recoverable challenges can build resilience. Continual activation without recovery creates biological wear.
- Strength protects muscle, bone, metabolic health, balance and independence. Muscle is one of the most powerful anti-frailty organs in the body.
- Sugar refers to metabolic regulation. Frequent glucose spikes, insulin resistance and visceral fat can drive inflammation and vascular damage. Protein, fibre, minimally processed food, lifting heavy things and movement after meals can all improve the metabolic response.
- Sociability belongs in every longevity prescription. Human connection has a measurable biology.
“If you’re consistently getting those five right, you’re influencing almost every hallmark of ageing we currently understand,” she recommends.
Biological age is an interesting lens through which to view health, but it’s not a verdict. At its best, it can encourage better habits and remind us that ageing is not simply something that happens to us.
The healthiest ageing strategies remain remarkably familiar: move more, build strength, sleep well, eat well and stay connected. Be curious about longevity science, but sceptical of anyone selling the promise of a younger number.