I think it's more breed specific along with the days getting shorter. I've had English Orpingtons mature just like they should in summers way hotter than this one has been. Ya know what they say, the waiting is the hardest partQuestion for my Texas folks!
Have you noticed your pullets and cockerels mature much slower in the heat?
I'm somewhat close to Lake Livingston and I have 11 pullets and 1 cockerel. All almost 25 weeks old. The cockerel started crowing and mating a week or 2 ago. Definitely a late bloomer- he didn't have male specific feathering until close to 18 weeks old. Only ONE pullet is laying. All the others are taking their sweet time. The weird part is I have a variety of breeds so I would expect at least more than 1 to lay by now.

