Each year we keep a few spring chicks & sell a few pullets/ or 1-2 yr old hens in fall. I feel people won't buy a hen over 2, so I try to sell them while they still have egg or breeder value. We generally eat or give away the male chicks. If a hen is still here at age 3, there's a reason, she's a pet, and she'll be staying long term. I'll cull a hen if there's an issue affecting laying - like an old hen with shell-less eggs. That's gotta hurt, so if calcium supplements don't work, I feel it's for the best to let her go. Also if a hen gets an injury that I think will be too difficult to treat effectively or cause long term harm, I'll cull her. ..... And, yes, it's very hard to make those decisions. However, once it's done, there is also some relief. (!. less birds to feed & clean, so less work, 2. knowing your hen is no longer in pain, and 3. a little pride in being able to make a meal from your own backyard.) Even if #3 doesn't apply, 1-2 can be comforting.
My 7 yr old EE is still laying well. It's OK that some of our hens stop laying for the winter, because we've got 1-2 pullets to get us through the lean months.