24 weeks old and still no eggs??

I have a 24 week old flock of different breeds. 2 SLW, 1 Australorp, 1 EE, 2 Brahma, 1 Silkie Mix, all pullets, 1 Mixed Roo, 1 Ameraucana Roo. Not one hen is laying yet. They free range, coop at night, and are on SS Layer and Breeder. I thought they were possibly laying in the bushes, so locked them in the coop for 3 days, and still not one egg. Any ideas, or is this normal? My RIR's started laying at 18 wks, but are from a different flock.

 

The Australorp, 1 of the Brahmas, and 1 SLW all have blood red combs and waddles, and have for 2-3 weeks now. I have heard the Australorp "singing", but with no results. Not sure I know what you mean about the squatting? I'm positive about the age.

 

Ugh!!! Of all of my chickens, that flock eats the most, by far. They better start earning their keep soon, LOL! I keep saying it'll be worth the wait, but the wait just keeps getting longer and longer.