I have to be honest and write I'm finding it quite hard watching them grow old.We plan to let ours live out their lives, and get some new chicks every 2 years to keep the laying going...we have them for pets as much as egg production
The hens status seems to change when they can't lay eggs anymore. While the young hens don't bully them as such, they do seem to take priority for food, both with respect to the roosters and the other hens.
Here the eldest now goes to bed early and doesn't charge out of the coop in the mornings like she used to. The changes seemed to have happened quite quickly.
If you watch your flock regularly it would be interesting for all chicken keepers to have more information on the behavior of ageing chickens. There just isn't much reliable information out there on this topic.