I would argue that the effective age of people vary with their behaviors and environment. For example, I've seen 60 year old in australian outback on horses do

I would argue that the effective age of people vary with their behaviors and environment. For example, I've seen 60 year old in australian outback on horses doing heavy work, as if they're 40. And I've seen 60 year olds in australian capitals barely doing anything of their day. Which do you think will go extinct first? I'm going to argue that simply "we are what we repeatedly do". Some people act old at 50, some people act young at 70. For example, my uncle in Europe has acres of property, works in it every day, goes dancing with the local "brotherhood" and would drink you under the table any day of the week. And he's close to 75. Trying to explain people with mathematics is similar to trying to explain women with science. It may work, barely. (no pun intended, just a cheeky joke)