we have some slow whites that are about 14months old and a new batch that are about 11 weeks.
We had planned to butcher and can some of the older hens for broth and soups, and keep some of the new hens to replace them... so is that not a workable idea?

at what age are they not edible for humans?

and Davey, we butchered some older chickens and they were so tough even after cooking for hours the dogs wouldn't eat them, lol, we now have a pressure canner to use..
such a learning curve..