I have 5 pullets that were born at the end of March/beginning of April. One is a purebred Polish, two are Barnevelder x (sisters) and two are EE (sisters). Only two (one sister of each set) have started laying - about 6 wks ago. These girls are now 31-32 wks old and haven't laid. I know the days are getting shorter but I've had pullets lay their first eggs at Christmas. There are not under lights and I'm not interested in doing that. Why would only one of the sisters start laying so much earlier than the other?