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I think there is an unwritten law that every article or policy discussion about the ageing population must begin with some scary statistics to frame the debate. So here are a few from the UN. Between 2015 and 2050, the proportion of the world’s population who are more than 60 years old will nearly double from 12 per cent to 22 per cent. In 2021, there were 17 people aged 65 and over for every 100 people aged 20 to 64 (this is the so-called “old-age dependency ratio”); by 2050, there will be 29 for every 100.
So far, so familiar. But what if these statistics aren’t a useful frame for the debate? What if “65 and over” is a bad definition of “old-age”? In fact, what if chronological age isn’t a good yardstick for ageing at all?
The only thing a person’s chronological age really tells you is how many years they have been alive. Policymakers fret over statistics like the ones above because they’re using chronological age as a proxy for other things they’re worried about, such as the number of frail or ill people who will need health or social care in future, or the economic and fiscal impact of fewer workers and more pensioners, and so on.
That would be fair enough if chronological age were a reasonable proxy for all those things, but is it? A paper published last month by economists Rainer Kotschy, David Bloom and Andrew Scott argues that relying on chronological age is “at best incomplete and at worst misleading”, because it provides “only limited information about the ageing process”.
Most obviously, people of the same age can vary hugely in terms of how frail or unwell they are. Using data from the US and England on the physiological abilities of over-50s, Kotschy, Bloom and Scott found that the healthiest 10 per cent of the population at age 90 are close to the same level of frailty as the median 50-year-old.
Average health and fitness levels by chronological age can also change over time. In the UK, for example, 70-year-old women in 2017 displayed about the same levels of poor general health as 60-year-old women in 1981, according to the Office for National Statistics.
If you are using chronological age as a proxy for when people stop working, that also varies a lot by country and over time (and is, of course, particularly sensitive to changes in the state pension age). How meaningful is an “old-age dependency ratio” that classifies the over-65s as “dependent” in a country such as the UK, where the proportion of them in employment has risen from 27 per cent in 2014 to 40 per cent in 2024?
As Warren Sanderson and Sergei Scherbov, lead researchers in this field, have put it: “should 60-year-olds in Russia in 1950 be considered to be as elderly as 60-year-old Swedes in 2050? If not, is there a better alternative?”
Sanderson and Scherbov’s proposed alternative is to define the onset of “old age” as the point when you have 15 years of life expectancy left. Through this lens, the past, present and future look very different.
In the UK, for example, which enjoyed strong increases in life expectancy up until the last decade, the number of over-65s increased by 8.3mn between 1981 and 2017, but the number of people with a life expectancy of less than 15 years fell by 7.4mn. And if you recalculate old-age dependency ratios with this definition of “old”, they are lower in all regions of the world except sub-Saharan Africa and Oceania (excluding Australia and New Zealand), and they are projected to rise much less steeply.
Of course, that might not be the right lens either — it will depend on the specific issue you’re worried about. Take questions about when people should be able receive their state pension. In recent years there has been a proliferation of new “clocks” that aim to measure a person’s “biological age” based on metrics such as proteins in the blood. Could they one day be used to determine each person’s state pension age, given that any system which uses chronological age or average life expectancy is unfair to poorer people who live shorter lives?
Scott told me he’s not sure people would accept that, even if the clocks became scientifically robust enough. “Can you imagine two people of the same age, same job . . . but one gets to [have their state pension] three years earlier?”
There isn’t one perfect metric that can replace chronological age as a measure of population ageing. But once you see the definition of “old” as something other than the number of years people have been alive, it begins to look more malleable than inevitable, and those scary statistics about the pace at which we’re ageing look more like a challenge than a destiny.
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