I haven't been keeping chickens quite long enough to have any ancient ones, but I do have an oldest hen.
This is Pecker, the only surviving chicken of my first flock. She is 3 1/2 years old, and still lays like the youngest of them. She's not the friendliest (which is to be expected of a Rhode Island Red) but she's incredibly smart. She rules the roost but likes to let my oldest rooster (who's 2 years younger) think he leads.
Some of the old timers on the site discussed such as couple years back. They had some birds and reported what they saw for an extended period of time. At least one party employed a restricted ration to slow growth. Also keeping birds calm would be something I would do. They selected for growth but not sustained activity. Muscles might also be stronger than what bones and joints designed to work with.
@sunflour she was a cross-breed. Much of the chickens outside commercial farms and the handful of breeders in a S.A. are a bit of this and a bit of that crossed with something else and here you go. We made up our own chickens down there lol
This is Mairah, a clean faced Easter Egger and my eldest and top hen. She's 7 years old and the sole survivor from my original flock. I free range so she gets plenty of exercise and foraged goodies. She also gets fermented feed, loves to be held and still gives me 3-4 eggs each week. I do not provide artificial heat or light during the winter months to give my girls a break from laying. She does not show her age, keeps up with the flock and is the first one each night up on the top roost.
I did lose a hen this past spring to stray dogs who got into my coop. She was 6 years old and was also still laying 4-5 eggs each week.
Lily and her two sisters are in their tenth year. She's a WPR and her sisters are a BO and a SLW. The BO and the WPR still lay during the spring. The SLW has evidently went through henopause. (She was molting and taking a dust bath in this photo.)
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Thank you. She's a sweet girl. She will give me the occasional eggs during the winter too but yes, I agree that not using supplemental light makes a huge difference. I was living without electricity when I started raising chickens so it wasn't even an option for me. I got my original flock as chicks and wasn't able to have a "proper" brooder so I used hot water bottles to keep them warm. They all survived to adulthood and laid very well through their first couple of winters. Her flock mates were all lost to a fox so she spent her time with the ducks I had at the time until I got more chickens. She even learned to evade the fox by heading into the pond with the ducks until I was able to dispatch it.
A lady I know with Orpingtons has a hen she started with and she is 12 years old...Calls her grandma...She loves all the chicks, but spends most of her time alone...She is a Big Buff...Nasty feathers..She looks old...Hangs out by the coop in a pot of dirt..She is really neat..
I think overall, the life span of a chicken depends more on living conditions rather than breed averages. You can have a chicken breed that is known to live past 10 years and stay generally healthy, but if you don't take care of them and their living environment, you can know that it won't live very long. I think we all need to focus on providing our chickens with a healthy life rather than getting caught up in life span averages.
Growing up - We had chickens that were about 5-6 years old when our german shepherd got to them and killed all but 1. They weren't laying very often by then, and the lone chicken went to my aunt who ran a feed store for a while. I believe she made it until about 10, when she finally died. (I don't know what from.) but they bulldozed over the pastures, feedstore, and house to make an apartment complex.
My Oldest chicken was two Buff Orpington one hen one rooster who lived for nine years!
She stopped laying eggs and he stopped crowing for some weird reason?
They died last winter but they were like great grandparents to my newborn chicks!
They weren't laying very often by then, and the lone chicken went to my aunt who ran a feed store for a while. I believe she made it until about 10, when she finally died. (I don't know what from.) but they bulldozed over the pastures, feedstore, and house to make an apartment complex. 
