I don't think subbing them all the time is a good thing... after all, they're still young, they should play easier games. Don't get me wrong, i have a lot of respect for you! you play since when it was possible to make Fabio Paim a great player... just like me....

Anyway i have a different opinion in out to get the best out of you're youg players
If you don't mind breaking a few rules you won't have any problem doing this: send all ouf your best young players to a feeder from a lower division, train that feeder and make them first team player all the time. this way has a good advantage: you get to make the trains for them, so they should evolve whell.
Another way (the one that I use) is simpler and it doesn't implies the break of rules: you have a reservs team right?? then use it!
But be smart! the more games they have, the better they'll evolve, plus, if the games are easy, i mean really easy, they'll evolve into super stars! How? get them to make friendly games(sorry about the speling) from 4 in 4 days, do it with really easy teams like "999" or whatever... if they win like 14-0 the players are sure to evolve greatly.
If you want you can do this in a bigger level and this is how they'll evolve the best, it´s a cheat though...: Go train a team from another league, any team you want. loan the players you want to evolve to them, then stay training that team and before every game get a new manager in the team you are playing against with. make sure the team you have the players loaned allways wins by a lot. I did this back in the fm05 with Catania, using loaned young player from Benfica. Two of them where described as "wonder kids" in the end of the season