A natural life span if everything works is about 100. Granted my great grandmother lived to be 101 (1845-1947), and decided to die, and did, on a dime, when her favorite eldest son died at 79, with her having no apparent health problems per se. She was sentient and ambulatory and active until her final exit. Or so my grandmother told me (grandmother was the youngest of the six who survived to adulthood).
So if the natural life span is about 100, why not get there intact? Is it really extending the natural life span or achieving the natural life span in relatively good shape what is motivating the whole stem cell thing. I don't see it as selfish to want that and don't see wanting that as being harmful to our children et al. Unless of course they just want our money and want to have less payout of benefits to old people. And that is understandable but craven. I prefer my craveness to theirs any day.
Actually it's about 40. That's when your immune system starts to shut down, because it's not needed anymore, as it no longer matters whether you live or not.