I have 2 leghorns that are 20 weeks and only one of them is laying right now. I have 2 barred rock that are 20 weeks and only 1 is laying right now. And I have 2 RIR and 5 Ameraucana that are 20 weeks that aren't laying at all.....So I think they just do it when they are ready. I'm trying to be patient.....It is so hard though!