I have 2 chickens that are 21 weeks old that are still on pedigree start and grow. I have 6 chickens between 14-16 weeks old that are also on start and grow. My question is when should I change their feed to laying feed and how could I go about doing that since they are all in the same pen. I've been told to never give a chicken under 20 weeks laying feed. Someone pls help.