24 is the age below which other clubs have to offer a fee for a player even if he is out-of-contract, as opposed to non-contract. At the moment we can refuse to sell if we're not happy with the fee offered. Once the player is out of contract (in Erhun's case at the end of the season) we can't stop him moving and the fee will be decided by a transfer tribunal if necessary. Erhun won't be 24 until after the end of next season.
I don't feel Erhun's lack of height is a barrier to him playing in the Football League, after all he's already been a pro at two Turkish Super Lig clubs. In the pre-season games we played against pro clubs I thought he stood out really well and the Palace fans on their "Holmesdale online" forum were very impressed, saying they couldn't understand why he wasn't a pro by now. (He also impressed against them in the pre-season game a year earlier.) My only reservation would be that he is so one-footed. He's scored more goals with his head than with his right foot!