Many production breeds don't even make it this long.
7 years is a good long life for the average chicken. Some can live a lot longer, but they don't all live into their teens.
Very interesting thread! So many factors come into play when putting an "average lifespan" on chickens. Every flock is different, every breed, all the genetics, environment in and around the coop and run, etc... This is a difficult question to really pin point over all. Some people will...