I have (2) Black Australorps but they are developing at different rates. One had a severe case of wry neck and took about 2-3 weeks of treatment to pull out of it. The other hen shot up in development however far past the rest of my girls all of the same age in size, wattle development, and comb development. We were afraid "she" was a roo for a little while.
Our first egg came 19 weeks. She started squatting at 18. She has been laying a little over 2 weeks now and gives us about 5/week at the moment.
Our other Australorp, the one who went through wry neck a couple of months ago, has not started squatting yet.