A healthy, well-cared for chicken can live well into the teen years. The girl at my local feed store had an old biddy that still laid well and raised a clutch of peeps every spring until she died at 18. That's the oldest I have personally known. The oldest hen I ever had was my beloved Alice - she was 11 when she died.
Chicken longevity is a bit of an evolving concept - in the past layers were lucky if they made it to two years old, then out went the old and in came the new. Now that more people are keeping chickens as pets and tending to individual health needs as opposed to general flock health, we are seeing older and older chickens, and I'm sure that trend will continue.