If you've got a good predator-free environment, it's not hard to keep birds to ripe old age. My oldest hen was 12 years old, the rest of her flock lasting until they were 8. This was without any special care. Roosters burn out much quicker though, and I've never been able to keep one in old age alive longer than the hens. :/
....unless you have hatchery hens with that "kill switch", that is. Then, no amount of fabulous care will keep them going. Their sucky genetics will win out over your best efforts. I've learned my lesson about that now. The ones I breed here or that came from good breeder stock have fared much better, but I've only kept my own flocks for about 8 years now, so longevity of the breeder stock that I began acquiring the following year after I began hasn't been well tested yet. My RIR x Buff Orp hen, Meg, who is out of exhibition stock, is 7 years old and still laying. Gave me an egg today, actually. She doesn't seem to have any real issues other than chronic bumblefoot on one foot.
I hope to have hens live as long as 12 like yours! That would be awesome.