If they're not exactly key players, you can always try to loan them out and choose a club with better staff and facilities.
That also has the added bonus that no-one can make a bid on them (and the idiot chairman accepting on your behalf) while they're on loan.
The way the game works any young player worth your time is a already star at 16 so you might aswell put the good ones in your first team and keep training them rather than try to make them into mediocre by loaning them out etc The training/potential/peak age system is quite bad/unbalanced/odd/not-so-good/unrealistic.