Well, I guess that depends, are we talking chronological age or something altogether different? We all should all be able to say how old we are with reference to the number of years that have passed since that fateful day we were born, although I do sometimes have to think about it as counting candles on the birthday cake became like staring at a forest fire some time ago! We can look younger than our years, or older.

However if one looks at various sites on the interweb one will find multiple measures:-

Some of the most respected biological age tests are epigenetic clocks, sometimes called DNA methylation tests. Other clocks incorporate external factors like smoking history, or chronological age into a biological age calculation.

To calculate body age add one year to your chronological age if your BMI is under 18.5 (underweight). Add two if it is between 25-29.9 and three years if it is more than 30. Subtract one year if your BMI is between 18.5 and 25.

Young at heart? – Here’s how to find out! 

Heart age https://www.nhs.uk/health-assessment-tools/calculate-your-heart-age.

However, there are so many variables that anything approaching something we could really depend on does seem far away. How well you chose your parents will be a big determinant, how much you smoked and for how long and how lucky you were to have avoided any nasties before you gave up will be important. Fitness does seem to be important but is difficult to define or measure accurately, certainly not well enough to put into an algorithm that can accurately measure risk and thus a number that might relate to an ‘age’ which presumably is a marker as to how long one is likely to live. I’m two years older wrt heart age than my chronological age but have never smoked, have elderly parents and eat a healthy diet and drink within the recommended level of alcohol (albeit more than zero which is sometimes quoted as the only safe limit!)

I’m sure we all know folk who don’t act their age and are forever teenagers or indeed those that act like their grandparents. You’re as young as you feel is a popular belief, or more prosaically you’re as young as the woman (or man!) you feel! Interestingly studies have found that marriage is more beneficial for men than for women, at least for those who want a long life. Previous studies have shown that men with younger wives live longer. While it had long been assumed that women with younger husbands also live longer, a 2010 study found that this is not the case!

My 90 year old mother still looks after the neighbourhood ‘old dears’ decades younger and my grandmother when in her 80s wouldn’t entertain ‘old boys’ in their 60s!

Recently studies have shown that maybe it’s all in the mind and that we actually think ourselves as being old only when there seems no option but to accept the numbers on the birthday cards!

Another great article in the Guardian reflects on a recent study that may be of some interest to you!

Nicola Davis Science correspondent

Perception of when old age starts has increased over time, shows study

As people get older, they revise the age they consider to be old upwards

None of us are getting any younger, but it appears the age at which we are considered old has moved upwards over the generations.

What’s more, as we get older we seem to shift the goalposts.

and this upward shift might be due to increased longevity, life expectancy and older age at retirement age etc.

“We should be aware that conceptions and perceptions of ‘old’ change across historical time, and that people are quite different regarding when they think old age begins, dependent on their age, their birth cohort, but also their health etc,” said Dr Markus Wettstein, co-author of the study, from the Humboldt University of Berlin.

Writing in the journal Psychology and Aging, Wettstein and colleagues report how they analysed responses to the question: “At what age would you describe someone as old?”, which is part of the ongoing German ageing survey that follows people born between 1911 and 1974.

The results from 14,056 middle-aged and older adults who answered the question between one and eight times over a 25-year period from 1996, when they were between 40 and 100 years old, reveals that the point at which old age is thought to begin has increased.

“For those born in 1931, the perceived onset of old age is 74 when they are 65. For those born in 1944 it is about 75 years when they are 65 years old,” said Wettstein, adding that while the study could not ask 65-year-olds born in 1911 when they thought old age began, models suggest it would have been at 71.

However, it seems perceptions are stabilising: while the team found people born after 1935 perceived old age as beginning later in life than those born between 1911 and 1935, there was no noticeable difference between those born between 1936 and 1951 and those born between 1952 and 1974.

Further, as people get older, they revise the age they consider to be old upwards.

“This could have to do with the fact that many people do not want to be old, so they postpone the onset of old age,” said Wettstein, adding that that could be related to age stereotypes.

However, it seems those born in later cohorts shift the goalposts to a greater extent: while people born in 1944 revised their notion of old age upwards by 1.9 years on ageing from 64 to 74, those born in 1934 shifted their view by less than a month between these ages.

The team add that while the perception of when old age begins was higher for women than men, and lower for those who had poor health or were more lonely, neither these factors nor education level or how old participants felt, fully explained their findings.

Caroline Abrahams, the charity director at Age UK, said it was well known that people tended to judge “old” as meaning at least a few years beyond their chronological age, even in their 70s and 80s, and that probably reflects the bad image of “old” in western cultures.

“This is a shame if it holds us back from living as full and happy lives as we could and should in our later years, because of us self-limiting our activities and aspirations,” she said.

Instead, Abrahams said the idea that we are “as old as we feel” is a lot more supportive.

“The truth is that chronological age is rarely a good proxy for anything and the sooner we realise that in our society, the better,” she said.

They found that as people age, their ideas of when old age started changed. At age 64, average participant in the German survey said old age started at about age 74 and at age 74 the average survey respondent said old age started at closer to 77, according to the study.

“At what age would you describe someone as old?” Perceptions of when old age begins might be prone to upward shifts because of historical increases in life expectancy and in retirement age, as well as because of better psychosocial functioning in later life. We investigated historical changes in within-person trajectories of the perceived onset of old age using data from 14,056 participants who entered the German Ageing Survey at age 40– 85 years and who completed up to eight assessments across 25 years. Using longitudinal multilevel regression models, we found that at age 64, the average perceived onset of old age is at about age 75 years. Longitudinally, this perceived onset age increased by about 1 year for every 4–5 years of actual aging. We also found evidence for historical change. Compared to the earliest-born cohorts, later-born cohorts reported a later perceived onset of old age, yet with decelerating trend among more recent birth cohorts. Within-person increases of the perceived onset of old age were steeper in later-born cohorts. The described cohort trends were only slightly reduced when controlling for covariates. Being younger, male, living in East Germany, feeling older, reporting more loneliness, more chronic diseases, and poorer self-rated health were each associated with a perceived earlier onset of old age. Our results suggest that there is a nonlinear historical trend toward a later perceived onset of old age, which might have meaningful implications for individuals’ perspectives on aging and old age.