I read (Raising Chickens for Dummies) that hens/pullets are born with the number of eggs they will lay already in their "ovum"... pre-determined.
I know people with six year old hens that are still laying? I am sure it varies chicken to chicken, but maybe it does vary breed to breed as well. I don't know.
I will look that up again....
Hens stop laying if they are ill... some of mine stopped for periods of time due to the heat during the summer.. some stop laying due to the shorter days, colder weather.
Don't lose hope.... I had an EE that stopped laying IN JUNE... (I thought due to the heat).... she just started again this week. (After a long and repeated worming of the flock for tapeworms).... (she's about a year and a half old now... two in the spring).
I had about given up on her, but due to her beauty was going to wait until Spring to see if she started up again then. I am overjoyed that she started up again laying her extreme Jumbo pastel mint colored eggs.
Hang in...