Exercise is much like calorie restriction in its effects on biochemistry - overwhelmingly beneficial, when compared against those who don't keep up the effort. Everywhere that scientists look more closely at our biochemistry, it seems, they find some positive change for having maintained a modest regimen of exercise:
The bottom line: over the long term, these sorts of changes add up to additional years of health. Exercise reduce the rate at which some of the cellular and biomolecular damage of aging accumulates, either by slowing the ongoing addition of new damage, or by modifying the processes of repair. In a future of rapidly advancing biotechnology, even a single additional year of time to wait for new therapies is a big deal. So swing the odds in your favor.
Here's another example from recent research:
Reactive oxygen species production increases during aging, whereas protective mechanisms such as heat shock proteins (HSPs) or antioxidant capacity are depressed. Physical activity has been hypothesized to provide protection against oxidative damage during aging, but results remain controversial. This study aimed to investigate the effect of different levels of physical activity during aging on Hsp72 expression and systemic oxidative stress at rest and in response to maximal exercise.
The key finding of this study is that, in people aged 60 to 90 years, long-term high level of physical activity preserved antioxidant capacity and limited oxidative damage accumulation. It also downregulated Hsp72 expression, an adaptation potentially resulting from lower levels of oxidative damage.
These things add up. Every extra year of healthy life you engineer for youself the old-fashioned way is an extra year in which you can benefit from future advances in biotechnology and longevity medicine. Helping to make those years possible now is an investment that will pay an impressive return.