I believe it's probably not "over-training" per se. I think it's competitiveness. Kids these days are technically sound and play at a higher level than probably you and I at this age (High School). Most have to be game-ready or risk losing their position to a kid that is. The only way to be game-ready and be consistent, is to prepare.
Kids that love the game and possess the desire to play at higher levels will push themselves to work harder than the guy next to them. It's to their advantage. Now, that might lead them to not train correctly, but I don't think it's over-training. Correct-balanced training can be executed on a consistent basis. It obviously includes rest, nutrition, and a good mental perspective.