The software programs that make our body run. . . were evolved in very different times. We'd like to actually change those programs. One little software program, called the fat insulin receptor gene, basically says, 'Hold onto every calorie, because the next hunting season may not work out so well. ' That was in the interests of the species tens of thousands of years ago. We'd like to turn that program off.
The problem with living so long is that we get used to it. We watch the mortals age and wither and die around us, watch the world change and decay. . . but no matter the hardship or the pain or the sorrow we suffer, we choose to continue living. Out of sheer habit, I think.