We still have them on grower feed with oyster shell(we were advised to do so by other members on other threads) so there isn’t a calcium overload for the non-layersWell it just may be the strain of chickens. I had some Light Sussex that didn't start laying till they were 39 weeks. Did a breeding on those birds and their children started laying at 35 weeks . it just depends on the bird. do you have them on layer feed?
Best,
Karen