Volume Oxygen max is one of the more significant markers, and rate of recovery, thats massive, susceptibility to injury is written into this, bone density of course, and another massive one, immune response. Under the microscope they compare cells with those of younger/older ones, and they look at the length of its tail - Up to twenty years longer/shorter! I believe that much needless ageing is as consequence to social indoctrination, and this has caused a segregation, other than merely the getting from A to B, of so called young people with so called middle aged, and older, people. In my view it is not even natural to think of ourselves as being older with the passage of time, and most certainly that is an ageing mindset. At sixty, ideally, one should still "KNOW" that one is of twenty years, and in contention still with the best in the world. I have teenage friends, thats odd/different, but remember this, I did not befriend any single one of them. In my opinion young people, socially, are drawn by youth, a person exceptionally young for their years hints at a possibility for their extended youth too. One girl, eighteen, even asked me out a short while back, perhaps she thinks Im immortal?? It would nt have been the worst thing in the world Had I of accepted , at least nineteen in every twenty relationships fail anyway, and I could have kept reminding her, that actually, I`m not immortal. There exists far too much both forward and reverse age prejudice, us thinking that we are somehow better than young people, and young people being obliged into reacting to this. With the right mindset, and the knowledge to back it up, they can all make a significant address to their otherwise rate of demise. They befriend me and in return I try to benefit them.