Defying the odds: the relative age effect’s absence among the best teenage football players in the world by Arve Vorland Pedersen:

The relative age effect (RAE) is the advantage of being born earlier in the selection period, thus being more experienced and more developed.

[…] In the 2025 U20WC, 287 players (57%) were born in the first constituent year whereas 217 (43%) were born in others, and in the 2023 U20WC, the corresponding distribution was 292 and 212 (58%-42%).

Among the CIES’s 200, 59 players (30%) were born in the first constituent year (i.e. 2005), whereas 100 players (50%) were born in 2006, 36 (18%) in 2007, and five (3%) in 2008.

[…] The selected ones are not necessarily the best prospects but ones who perform best among their often less physically developed peers.

[…] Club scouts, as well as scouts selecting players for regional and national teams, should be aware that many of the players that they select may be selected largely due to their physical development, not their skill.

As a kid, I was always jealous of the kids of my similar age who were put in the age group below because of that physical development advantage. You are just stuck on the bench in the lower rung of the club when you are small and scrawny.