I didn't include the U17 level because it's too young, in the past, it was actually called U16. The main youth categories are U21, followed by U19. Many U19 and especially U21 players are already professionals, whereas U17/U16 players generally aren't. It’s a much more reliable indicator. At the U17/U16 level, on the other hand, there are many players who will never turn professional.
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