Imagine, for a moment, that you had no birth certificate and your age was simply based on the way you feel inside. How old would you say you are?
Like your height or shoe size, the number of years that have passed since you first entered the world is an unchangeable fact. But everyday experience suggests that we often don’t experience ageing the same way, with many people feeling older or younger than they really are.
Scientists are increasingly interested in this quality. They are finding that your ‘subjective age’ may be essential for understanding the reasons that some people appear to flourish as they age – while others fade. “The extent to which older adults feel much younger than they are may determine important daily or life decisions for what they will do next,” says Brian Nosek at the University of Virginia.
Its importance doesn’t end there. Various studies have even shown that your subjective age also can predict various important health outcomes, including your risk of death. In some very real ways, you really are ‘only as old as you feel’.
Given these enticing results, many researchers are now trying to unpick the many biological, psychological, and social factors that shape the individual experience of ageing – and how this knowledge might help us live longer, healthier lives.
This new understanding of the ageing process has been decades in the making. Some of the earliest studies charting the gap between felt and chronological age appeared in the 1970s and 1980s. That trickle of initial interest has now turned into a flood. A torrent of new studies during the last 10 years have explored the potential psychological and physiological consequences of this discrepancy.
One of the most intriguing strands of this research has explored the way subjective age interacts with our personality. It is now well accepted that people tend to mellow as they get older, becoming less extroverted and less open to new experiences – personality changes which are less pronounced in people who are younger at heart and accentuated in people with older subjective ages.
Interestingly, however, the people with younger subjective ages also became more conscientious and less neurotic – positive changes that come with normal ageing. So they still seem to gain the wisdom that comes with greater life experience. But it doesn’t come at the cost of the energy and exuberance of youth. It’s not as if having a lower subjective age leaves us frozen in a state of permanent immaturity.
Feeling younger than your years also seems to come with a lower risk of depression and greater mental wellbeing as we age. It also means better physical health, including your risk of dementia, and less of a chance that you will be hospitalised for illness.
Yannick Stephan at the University of Montpellier examined the data from three longitudinal studies which together tracked more than 17,000 middle-aged and elderly participants.
Most people felt about eight years younger than their actual chronological age. But some felt they had aged – and the consequences were serious. Feeling between 8 and 13 years older than your actual age resulted in an 18-25% greater risk of death over the study periods, and greater disease burden – even when you control for other demographic factors such as education, race or marital status.
There are many reasons why subjective age tells us so much about our health. It may be a direct result of those accompanying personality changes, with a lower subjective age meaning that you enjoy a greater range of activities (such as travelling or learning a new hobby) as you age. “Studies have found, for example, that subjective age is predictive of physical activity patterns,” Stephan says.
But the mechanism linking physical and mental wellbeing to subjective age almost certainly acts in both directions. If you feel depressed, forgetful, and physically vulnerable, you are likely to feel older. The result could be a vicious cycle, with psychological and physiological factors both contributing to a higher subjective age and worse health, which makes us feel even older and more vulnerable.
Stephan’s analysis, which is now in press in the journal of Psychosomatic Medicine, is the largest study of the effect of subjective age on mortality to date. These large effect sizes demand close attention. “These associations are comparable or stronger than the contribution of chronological age,” says Stephan.
Put another way: your subjective age can better predict your health than the date on your birth certificate.
With this in mind, many scientists are trying to identify the social and psychological factors that may shape this complex process. When do we start to feel that our minds and bodies are operating on different timescales? And why does it happen?