I don't trap nest, or seriously evaluate each hen for her production levels, so it's more about my 'flock average' here. The EEs and French Marans are easy to determine, but all my brown egg layers, not so much.
Mary
Many chickens will die by three or four years of age, although there are some who will live much longer. My oldest hens have been ten years of age, and weren't laying eggs for some time before becoming ill.
My youngest pullets dying of reproductive problems were one at six months, and recently...
Most hens will produce fewer eggs as they grow older, and there will be big differences between individuals in the flock. Given good care, diet, etc, genetics and luck matter. Predation may remove some hens, so they aren't going to reach their full lifespan. Then nearly nobody breeds for...