Thought I'd take a look at the numbers from what used to be Ann Trason's race in my old backyard in the East Bay hills. Until I coincidentally ran some of the still-marked trails later on the same day this year, I'd completely forgotten about this race, or rather hadn't thought "hey it's October in the East Bay hills, when's Fire Trails" which come to think of it I guess is forgetting. (Hey, sue me. I've been in another city in medical school.) I was sad not to have used the chance to stop by to see some friends, but not sad I didn't enter; had no time to train anyway. Here's a scatterplot of the results
What those numbers above mean is that for this curve (with a decent R^2 value) male runners gain 4.3 seconds on their mile split in this race per year of age.
This is a little more pessimistic than the claim that runners keep their times until their sixties, as argued by many, most recently and famously McDougall in Born to Run. More interestingly, the women were all over the place
with a much worse goodness-of-fit score that predicts only a 1.7 second gain on mile split per year (below)
. This is the trend I'd expected ahead of time, but not to this degree! Being all over the place is emphatically a good thing because it means that race results for you ladies are much less predetermined by age than for us men, and on top of that your time increase per year is smaller. Whether this is a result of universal human biology (women innately resemble fine wine) or something to do with selection (e.g. women start racing later in life, or are more likely to interrupt racing careers with more-traumatic-to-female-physiology childbearing which can be recovered from, and so the times show that) is another question.