The reason he looks like that is in fact because of gender. He looks like a cockerel, and cockerels usually tend to mature rather slowly as compared to pullets. He should fill out nicely in a few more weeks, nothing at all wrong with him.
~Casey
Ok heres a follow up to what you said...if he is indeed a Roo, then should I assume that the three others are pullets? Those in the pic are the first four we got, and after thinking we might have 2-3 Roos, we went back to the breeder and picked three more that look more like pullets. With Smoke being the only one feathering so slow, does that mean he's the only he? Any insight is helpful.
~Ashley