Well then you aren't gonna find any Prem clubs who've brought through at that age because there are boundaries which you cant' cross unless you wanna be hit with transfer bans like Chelsea had because of the whole Bertrand Traore exploitation.
Scouting still have a responsibility to cater within a specific age group and that includes all u21 players, globally.
Bit of a pointless debate when you want to solely focus on players it's illegal for clubs to conduct in plus I doubt any of us here know a single 13....14....15 year old player outside of Liverpool.
It is pointless to mention SA region gor Academy when we can’t sign anyone below 18, presumably if they are any good then they would be in an established academy such as Benfica, Porto, or some where in Spain by then.