Probably your crossing is still set on manual. If you're not used to that you should try semi .
As for youth. Form plays a role in it. If your 25 year old is getting high grades he may get improved. Are you playing your 18 year old regurarly, what's his form and morale? Could also be he has nearly reached his potential, thus grows more slowly. Is this a scouted player or a 'real' one?
Thanks for help - he is a 'real' player: Ravel Morrison at Man United. Have played him at least 10 times - though mostly as a sub. Maybe that's the problem, but seen other players improving even just on the bench (youth goalkeeper for example)
Seems odd that you can't see it somewhere.