Interesting question. I am not a biologist, but I believe I read that cells have a sort of "internal clock", modulated by certain enzymes. Normally cells reproduce in a certain way, but these enzymes deplete over time, such that at a certain point the cellular structures don't reproduce in the same manner as before. Hence, "aging". So, sure I am all for finding treatments for Alzheimer's and so on, but aging itself, as outlined above, is just really an evolutionary necessity. Stephen King treats this sensitive topic well in his novel, 'Pet Sematary', dealing with both the human resistance to, and the biological necessity of, death, including the aging process leading into that. Personally I find great comfort in the idea that even if however many millions of years from now, all or most mammals, including humans, will be extinct, some of our genes won't be, just as for example birds have some of the genes the dinosaurs had. The individual may be here for only a short time, but the genes she carries are far more transcendent.