Bone mass increases, muscle to fat ratio conforms to work.
Yep. Hard work in my youth has served me well later--I have only broken a couple of fingers, despite some pretty harrowing experiences, and I'm a great-grandpa now.
The problem with the BMI calcualtion is that it is based on height and little else. If body fat was the metric, the measure would be more fair. Either way, I do not think physical characteristics should be taxed--the State does not own me, at least in theory, the Government works for me, at my consent (which is diminishing rapidly).