Is that so bad, though?
Let's say, hypothetically, that if you spend an hour exercising each and every day for 40 years, you can extend your life by an extra decade. Assuming a constant 8 hours of sleep daily, that's a four-fold return on investment!
Of course, due to the effects of aging, it very well could easily take me twice as long to do anything, and I could easily get only half as much enjoyment out of it. Sure, I keep pushing that number higher, but by a self-assessment of how good my life is, I'm only breaking even. Considering the risks associated with aging, is it even worth the investment?
My grandmother has said many times that the only thing wrong with her is that she hasn't died yet. She's well into her 90's, with no serious physical deterioration, but life has gotten boring. Her life-long friends have all died, and many of her new friends have died, too. Her children have grown up and moved on, and so have her grandchildren. She's traveled the world multiple times, and gone on every adventure that she wanted to. She was expecting to die twenty years ago, having lived a complete and happy life.
Now what's left? Seeing yet another round of new miracles being taken for granted by a generation that assumes such technology is a basic necessity for life? Watching $THIS_GUY slaughter $THOSE_GUYS in the name of $SUBJECTIVELY_JUST_CAUSE? Spending another year alone in her home?
More personally, I have a medical condition that will deteriorate rapidly when I hit about 50, and faster if I partake in strenuous exercise. The only treatment option includes the term "replacement vertebrae". Is it somehow morally wrong for me to plan my life such that I spend every waking moment now using my limited health in ways that I enjoy the most? I doubt I'll survive as long as my grandmother, and my condition effectively assures me of problems by that age, anyway. Hitting 75 and signing off sounds like a good plan to me.