I have 2 production type brown egg layer pullets (breed: Isa Brown) I think they're about 5 months old. One is approaching hen size and is clucking. The other is half her size and still peeping, and is behind in development in every way. I know that it is not lack of food, because I feed those two specially. What's up? She's perfectly happy and healthy, she just seems to be 3 months younger than her buddy!