The researchers compared the results of cyclists in the study against each other and also against standard benchmarks of supposedly normal aging. If a particular test’s numbers were similar among the cyclists of all ages, the researchers considered, then that measure would seem to be more dependent on activity than on age.
As it turned out, the cyclists did not show their age. On almost all measures, their physical functioning remained fairly stable across the decades and was much closer to that of young adults than of people their age. As a group, even the oldest cyclists had younger people’s levels of balance, reflexes, metabolic health and memory ability.
No, this isn't like Forrest not showing his age, that's different.