See Jane Run. See Her Run Faster and Faster - NYT

Men, as might be expected, get slower as they age. At a recent five-kilometer race in Pine Beach, N.J., which drew nearly 1,000 runners, the fastest man was 24 years old and the men’s times increased with each five-year age group.

But the women were different — their times were all over the place with older women beating younger women in almost every age category. The fastest woman was 37 years old; the fastest woman in the 45 to 49 age group beat the fastest woman in the 20 to 24 and the 40 to 44 age groups.