I haven't had to cull any yet, but my grandma and aunt always bought old laying hens to butcher. We referred to them as "stewing chickens" and used them for chicken noodle soup or chicken & dumplings or the like. That's what I have planned for many of my hens when they get too old to lay. (tho' not all of them 'cuz some I'm way too attached to!) Used to be you could buy them in the store marked as a "stewing chicken" too... I remember them being right next to the "frying chickens" (aka young) in the refrigerated sections.