As any animals, with age, your chickens too will first slow down the number of eggs they lay in a year and then completely stop. A normal, healthy, buff orpington will lay between 110 and 160 eggs in a year. They lay eggs throughout the year, including winter. It might be a good idea for you to keep a record of how many eggs they are laying/week and see if this is decreasing slowly over time or not.
Chickens do live to an old age, so it is unlikely that yours are starting to slow their egg laying rate at this point.
