In our setting predators do the job - hawks do lions' share (LoL) and foxes the rest. So agingn chicken does not happen. Although we had a rooster - a tiny one, which had incredible surival skills - was over 10 years, killed 2 bigger roosters himself, numerous unobedient hens, survived direct fox attack and dodged hell knows how many hawk strikes. Eventually went blind and had to part with his head out of mercy.