They are 18 months old. They started laying when they were about 6 months old.
That is good information. Some pullets will skip the molt their first fall/winter and keep laying until the following fall no matter how short the days and without supplemental light. Sounds like that is what happened to yours. You probably have dual purpose "production" breeds.
The normal cycle is that adults molt in the fall when days get shorter and stop laying. That's instinctive, their instinct is to lay eggs and raise chicks during the good weather months then replace worn out feathers in the fall and use the nutrients they would use for eggs to grow feather instead. Then when the days start to get longer it's a sign that warm weather is on the way so they start laying again.
But we domesticated them. We started breeding for more egg laying and less going broody. We feed them so food is plentiful year around. We provide housing to protect them from the weather and may even provide extra lights or heat. Many still have those basic instincts but by breeding and the way we manage them pullets may lay through their first winter. Hens may never go broody or some may even go broody in the middle of winter.
It's hard to say for sure what chickens will do any more. It is pretty consistent if you don't mess with light that adults will go through the molt in the fall, maybe start in September, maybe December or in between. Some hens will wait until the days get longer to start laying after the molt is finished, some start pretty soon after the molt is finished. I've had some finish the molt and be back to laying in November or December. Some wait for warmer longer days. Since the days are getting longer already and your pullets laid through the shortest days last winter I would not be that surprised if you saw eggs pretty soon, but it may still be a few months away. You just don't know for sure what a hen will do.