The way I monitor my aging is by comparing myself to my ancestors.
I compare what they looked like, behaved like, mental attitudes, involvement and satisfaction in life, health challenges, etc.
I mostly compare to my parents, grandparents, aunts and uncles.
So far at my age of 53, I am about 20 years younger than they were at 53.
I have none of what they have or had so far.
arthritis, depression, heart disease, alcoholism, gall bladder disease, physical inflexability, lack of stamina, non evolving life goals, terminal cancer, chronic acid reflux, menapause sympstoms, obescity, over whelming allergy, chronic use of pharmaceutical drugs, death.
I would not gauge my age on a standadizedd test.
I still act like a 33 year old, although granted don't look quite a good.