I think your hens would do much better if you were to give them feed formulated for laying. It will be labeled 16% layer pellet or crumble. I find I have less wasted food when I feed pellets. In regard to the hen with the "sag" could you submit pictures. I'm sure that with additional information someone will have an answer. The right age for eating is dependent upon breed and personal preference. I have butchered old birds for stewing hens and 2 lb cockerels for "cornish".