I agree with separating cockerels as soon as possible I would also suggest feeding them a higher protein feed than the young pullets for longer. Its good to separate for a variety of reasons. One is that a good roo will let his girls eat their fill then take what he can get. I prefer for my boys to "bulk" up if they can and removing girls from the equation helps a little with this. Without females to initiate the chest thumping so to speak the boys usually get along quite well. Mixing ages is always problematic though regardless of gender.