I hate to play Semantics Nanny, but it's time to nip this in the bud.
Dougdirt is right: "Old for the level" and "young for the level" are scouting terms, understood to be a comparison of the player's age to the league average age. That's it. That's all.
If you want to say that a collegiate top-ten pick should have advanced farther by now, say that. Say his development is struggling. Say he's not on the star track. Fine. But don't try to redefine the term "old for the level."