From a recent article on the NYTimes
The aging effect is inevitable, and now runners can even track what to expect. It is as if there was a time clock for aging, and unlike nonrunners — who have only things like wrinkles and gray hair to go by — runners have an exact schedule that will predict how their performance will decline.
That schedule is on the website of Ray Fair, a professor in the economics department at Yale, who was inspired to find the patterns of slowdowns when his own running performance began to decline. The result is a table. You can put in your best time ever for an event, say a 10-kilometer race, and how old you were when you ran it. The table then shows how fast you could have run it when you were younger and how fast you should be able to run it now and as you grow even older.