From Thomas C. Goodhart
The Girls (whom I have written about before) as they are commonly referred to around here, Ila and Lisa, are five and one-half years old, which in chicken years is pretty up there. On average the typical laying hen lives one to three years before she is culled. For commercial/economic reasons they usually have one to two good seasons of egg laying before they are retired. In comparison to contemporary chickens bred and raised for meat who on average are slaughtered at six to eight weeks, one to three years is long. How long an average lifespan a chicken would have if it did not become dinner depends upon its breed and type and obviously overall health but they have been known to live into their mid to late teens. Nevertheless, nearing the six year mark, the Girls are certainly on the upper age range of the average chicken.
Many folks who have not had much contact with live poultry will often ask how many eggs they lay a day. Again this depends on breed and type but for the most part a hen in the prime of her laying years—one to two seasons—will often lay one egg a day which can add up quickly enough to nearly 300 eggs a year. As she ages she will continue to lay but will produce fewer eggs each season. For the Girls, Ila even as a five-year-old hen was laying an egg just about every other day since early February with only recently entering a molting stage or resting period where her energy is redirected and she replaces her old feathers with new ones. Not bad for an older bird. (Incidentally, Lisa has some reproductive health issue and is no longer laying but she does well with providing Ila company so she certainly earns her keep.)