Jörg Seidel for Goalimpact:
Abstract: We found a strong Relative Age Effect in youth football. Yet many of the players that benefited from their relative age seem to fail to move to senior football because they lack their advantage among grown-ups. Football club could increase the efficiency of their youth programs substantially, by selecting player according to their talent rather than relative age. The minimum Goalimpact a player needs to achieve to have a realistic chance to become professional football player is 80. Yet older players often stay in business slightly below that age to.
Fascinating analysis, if somewhat obscure for most.