Yup. A study by Kings College in London examined muscular power as it relates to mental aging.
While strength obviously contributes to better physical aging (an easier time getting around and such), the study seems to show that those with powerful legs--the largest muscles in the body--have sharper minds as well.
Researchers studying more than 300 sets of twins over the past ten years found that those who had the sturdiest legs a decade ago showed the least deterioration in mental capability over time. If one twin had been more powerful than the other ten years ago, he or she tended to be a much better thinker now, performing about 18 percent better on memory and cognitive tests than the weaker twin.