Living longer would be nothing but a good thing for me. I'd love to have a run that long. Reach my prime, and then stay there for a long time. It's true though, something like this would require radical rethinking. Everyone should NOT be able to do this, or at least not to extreme degrees. At any rate you'd have to regulate population. Like, one child to a household. Once the kid is out and about, both parents have to undergo reversible sterilizations.
Seriously though, exciting stuff. Understanding why the human body degrades with age and eventually stops working, and then fixing it.