I need to be "edjumacated"....
This is my understanding, please feel free to correct it.
In US Soccer the age "bands" have a clear and fixed rule. Specifically, that a player can ONLY play UP. Meaning that a 9 year old can play "UP" on the 10 year old or 11 year old team, but cannot play "down" onto the 8 year old team. To my knowledge that extends throughout all of the strata in US Soccer.
How does it work in English football?
I ask because Koscielny, Age 33, is playing nearly full games with U21 and U23 squads...
How does it work in English / European Football?