I just adopted 5 pullets each 8 weeks old. I have them on Grower Feed. I need to switch them to Layer Feed at about 18 weeks right? And what will happen if my older hens, 1 approx 10mo. and 1 at approx 2 yrs. eat the grower food? Will they put on too much weight? Should I try to keep it seperate? And will it hurt the 8 week olds if they eat the layer?