I don't have the paper to hand, but I remember there was research a good while ago that showed - just like the young have growth spurts - there is an analogous process as you grow older. Ageing spurts - not all that desirable but there it is. Actually just looked it up and here it is:

https://www.sciencealert.com/our-bodies-age-in-three-separate-shifts-according-new-blood-tests