I've got a four year old Welsummer and a five year old SSH bantam. They are here to stay, one is very friendly and the other one was my oldest Welsummer and most reliable Wellie that still lays an egg for me.
Most of the time I usually sell two year olds just to make room for the girls I want to keep. If they don't have the disposition, they are the first to go. If they are not the color of egg I want to keep, they are going anyway. If they have too much speckles, they go too. And I cull hard as well.
SKE, I don't worm as often and if they need it, they will get wormed.