My BA began laying aroun 21 weeks (don't have your other breeds). I've read of some breeds laying as early as 17 weeks or so, while others don't start until around 26 weeks - so it varies, even among the same breed. Watch for comb and wattles turning really red, and some squatting behavior when you go to handle them... Egg laying usually starts shortly thereafter....
Strange, isn't it? Just sitting down watching the little devils doing their own thing is a very peaceful pastime.
When I was a kid there were hundreds, nay thousands of chickens on our farm. I never paid them any more
attention than if they were grass. Now I sit and watch. Amazing what a few dozen years will do for you.