It's interesting, and it kind of works to break it down this way. I didn't fully articulate what my concern is in my other comment, my question is how do you account for situations in which the same person in the same activity would be on opposite ends of the age gap depending on where they play.

A child born late in the year would have the most advantage in school sports, even say just PE class all the way up to the varsity team in high school, but that same individual (particularly as a younger child) would be on the bottom end of the age gap advantage in a city sponsored league that uses the calendar year