Most folks report lowered egg frequency by 3 yo, and average longevity of about 10 years. But I've lost 2 of mine at 2 and 2 1/2 yo due to natural causes. And there are rare reports of a chicken living up to 18 years! But most sources report a hen can lay eggs for years, but the frequency decrease with age.
Depends on the breed really. Sexlinks and production breeds (hatchery sourced) lay a ton for their first 2 years, and then production dramatically drops off. They tend to be fairly short lived, usually about 5 to 8 years. Heritage breeds from good breeders will lay fewer eggs per year, but will be regular producers for most of their lives. They tend to be longer lived birds, averaging about 10 years or more.
