Just make sure you don't try to make an entire team full of young players, I've already seem a couple of guys making that mistake. You should only be worrying about age/youth at the 1 or 2 position(s) you plan to train. You simply can't train all 5 positions effectively. Plus you have several years to build a team to compete at the highest levels and I would imagine that not more than 1 or 2 of the players you start with will still be on the team when you get there..