At around 6 months of age. Not too much you can do to speed it up that I'm aware of, maybe someone else will have some tips for you. But, since they'll be six months old in the depths of winter when they days are their shortest, you should set a light up for them to come on about 3-4 hours before sunup or stay on 3-4 hours after sundown -- 14 to 16 hours of light will encourage egg production when they do start to lay, and you'll get more eggs that way during the winter than if they didn't have the light.