@Aegon..."...it's very apparent that the best 9 and 10 year olds are not necessarily the best 11, 12 or 13 year olds.
Many kids who are in the Jets or TSP in 13's and 14's were not the best kids in their early JDL/SAP years."

I think it's fair to say that likewise the best 11, 12 and 13s will not necessarily be the best 15, 16 and 17 year olds too


What you said also checks out with statistics from Germany's development system, that shows next to no kids who received specialised (SAP/JDL type) training at a young age make it far in their football endeavours, the majority of those who do make it in their system apparently only begin "proper" coaching from the age of 17 and upwards

Details in this documentary you might find interesting: https://youtu.be/3beI0f8G-3A