It's probably wisest to hold off on the high protein food until he's about 18 months old (after that though, it's probably the best thing you could give him!).
In the meantime, a food that's high in meat content and with a protein level in about the 24-26% range would be more ideal. Since he's been on CS, a food that's something other than chicken/turkey based would give the best variety... there are several in the Timberwolf range if that one takes your fancy (a very good food, though somewhat more expensive than many).
Not sure, or just haven't read them? Read the Rules before you post please.