Not many CBs break through in their teens though, unless they are exceptional. Its a position that needs a bit more maturity and experience, not to mention a bit more physicality. One of the things the Academy system does not address well in my opinion, works well for FBs, MF, wingers and to some extent strikers, but CB and GKs not so well. Martin is that the age now where he should be breaking through, no idea what went wrong at Palace, he was looking good in the Championship last year, at least as a decent back up, maybe Eastleigh to PL is a step too far.