That's only if they are laying and putting all that stress in their bodies. It should actually be closer to the same comparison of a small. 10-15 years should be the norm, not the exception. Or an average of 5.33 years has been suggested.An old Post but I was wondering myself. From what I have found, it varies a little bit by breed of chicken. I put this together based on Buff Orpingtons. This is based on experience, not some scientific formula that I developed.
6 months of age = 12 years of humans age
1 year = 18 years old
1.5 years = 24 years old
2 years = 30
2.5 years = 35
3 years = 40 years old
more of less, after this multiply actual age by 10 and subtract 10. so a 6 year old chicken would be about 50 years old. (6 x 10 = 60, 60-10 = 50)
A 13 year old chicken, though rare, is possible and would be about as possible and rare as a 120 year old human.