How to get reserve team to play in a real league.

I've been playing with the editor to try and get my reserve team to play in the english league 2 (lower active english league). i've got them to appear in the league and they have fixtures etc, but none of the players i put in seem to be eligible to play. my reserves also comes labelled at u18's, and my u18's is listed as reserves.

have i just balls'd this up?

could someone give me a brief description on how to do this right please.

thanks for your help