I'm from a completely different climate, so I can't tell you about any regional things to look for.
I do know that my English Orpingtons took a little over 8 months to make their 1st egg. (My bantam orp only took 4.5 months.) Less daylight & cold temps keep many of mine from laying in the winter and will definitely delay the 1st egg.. Some people add artificial light to increase production. (It's the # hours of light, not really the heat.) Some of my Easter Eggers & Cream Crested Legbars just started back up a few days ago. (not all) We simply do not see blue eggs here in the winter.
If it's warm there, could something be eating the eggs? like a snake?
Are the combs red like a hen or still pale?
Do the pullets do "the squat" when you pet them?
If the comb is red, have you checked the vent?
Any signs of leg mites, feather mites, lice?
Anything possibly stressing them.?
Feather loss? (won't lay eggs if they're molting.)
Just some ideas. It could simply be slow maturation plus winter.. Birds hide illness very well, so just look them over carefully to be safe.
You can also just try the carrot & the stick approach.
(Carrot) Throw some veggie & kitchen scraps out in the run.
(The stick) Tell them they're going to provide dinner one way or another.
