From my experience, it varies from bird to bird. I have a Calico Princess that started laying at 17 weeks + 2 days (since she started to lay 2.5 weeks ago, today was the first day she didn't lay). One of my Barred Rocks started laying at 18 weeks + 5 days. I also have some that are 21 weeks and don't look anywhere close. My SLWyandotte's, Buff Orpington and Barred Rocks were all laying by 24/25 Weeks Old (I collected 5 eggs from my 6 layers today and typically get at least 4 eggs each day. Every once in a while I will get 2 eggs, but that's rare). All of my birds are let out of their hen houses at 7am and get locked up at dark around 5:30 and I don't use any supplemental lighting. I truly believe it varies bird to bird. Of course there are other factors involved, but the main difference looks to be individual, at least from what I understand from my 11 pullets (obviously I don't have a lot of experience, so I probably should have started with that tidbit of helpful information). A lady that works at my local market said that switching her pullets to a layer feed is what made them start laying, so answers vary about as much as the birds do

Thank you for sharing pictures. You have some gorgeous girls!!! Your marans and barred rock are looking nice and "reddy" (ready), so fingers crossed ! I'm not familiar with the Ameraucana or polish. Is the gray bird with the black head your Ameraucana? That bird is stunning! I am in love! Is the red bird in the pictures your Orpington? I only ask because she looks darker than mine, but she's absolutely gorgeous too! I love your flock!