Co-ed sports for kids that train together demonstrate this well. I was a competitive swimmer from the age of 5 to 18. Girls and boys received the same instruction from the same coaches, did the same number of laps in practice, etc. Before puberty, there was no difference in times between girls and boys. At about 10-11 years old, the girls started getting faster than the boys. But at 13-14 years old the boys became faster than the girls. Both of these correlate to when both groups reach puberty.