A lot do gymnastics quite early too (as in, toddlers lol)
I found an article ages ago talking about development of Ice Hockey players
How at ages 4-8 anyone could participate, from 8-12 they would cull about 50% of athletes as would keep doing this right until the end of teens. Progressing only those who showed potential (both physically and mentally)
It was quite interesting. Sort of like "natural selection" for sports