A study of people born within a year of each other has uncovered a huge gulf in the speed at which their bodies age according to this article on the BBC.
If older people perceive themselves to be younger than their chronological age and younger people are physically older than their age, then adjusting environments to accommodate physical change (i.e. Age-Friendly) becomes even more critical.
The report, in Proceedings of the National Academy of Sciences, tracked traits such as weight, kidney function and gum health.
Even at these relatively young ages, people with older biological ages tended to do worse in tests of brain function and had a weaker grip.