That sounds like a seasonal issue, not an age issue. Fall molts and shorter days can both effect laying. As pullets, they aren't as effected. As adult hens, you see the normal seasonal rhythms of their laying, when going broody, molting or short winter days can effect them.
Some people choose to add supplemental lighting in winter and some people don't. There have been a lot of threads on the pros and cons of supplemental lighting. You might want to check them out. Otherwise, laying should pick up again in the spring, when the days get longer.