In my professional life, I study neurodegenerative disease, the mechanisms of aging, and what the two have in common. I was reading through a textbook on aging a few months ago, and I came across an interesting series of graphs.
The first graph showed the average cardiorespiratory endurance of Americans at different ages. It peaks around 30 and goes downhill from there. But the author of this chapter was very intelligent; he knew that averages sometimes conceal meaningful information. The second graph showed two lines: one representing a man who was sedentary, and the other representing a man who exercised regularly for his entire life. The data were from real individuals. The endurance of the first man basically tracked the national average as he aged. The endurance of the second man remained relatively stable from early adulthood until the age of 70, after which it declined noticeably.
We aren't taking care of ourselves for nothing, ladies and gentlemen. We're doing it because the stakes are high. Just look at Jack LaLanne, the fitness buff. He's been working out regularly and eating a whole foods diet since before I was born, and he's still pumping iron every day at 93.