TBH, I couldn't care less about my reserves... I treat my reserves as a transition team where those who aren't good enough for the first team go above the age of 18... while I keep anyone below the age of 18 in my youth...
Besides, if good enough, some u18 gets picked automatically to play in the reserves if you have a manager for reserves...
I only have about 6 players in my reserves, they're all over 18 and aren't good enough or ready to play for the senior squad, and when reserve matches take place, the reserve manager picks some u18 in to place.