IIRC There is also a discontinuity when it comes to the histogram of ages of marathon runners, because runners are binned into age groups and there is a more runners at the youngest ages of each group, I guess because it’s younger runners in each group that are more likely to run if they feel more likely to place well in their group
I think there's also the opposite – there are a number of places in large marathons allocated for "good for age" entrants, which I would guess are more likely to be taken up by people at the younger end of those buckets.
