I've had lots of chickens who didn't start laying until they were 35 weeks old! In fact, one chicken was 50 weeks old when she laid her first egg! (Yes! I said 50 weeks!) I hatched her from an egg so I know she was that old! Ha! Just thought I'd tell you that I did read once that it's actually better if the hen is older when they start laying. But, some breeds mature later than others. I think Marans are ones that are a little later to start laying, so just wait. I also agree with Brucifer, the shorter daylight hours of winter will take the pullets longer to lay.
Haha, the record here is 44 weeks, heritage line Barred Rock hen; she broke the previous record held by my 9 year old EE hen, June, who laid her first egg at 40 weeks. I was about to pronounce Zara a complete dud until she finally popped one out in her 44th week. I guess it could be worse, HA!