I got a first egg from one of our Plymouth Rocks on 8/20/2010 and she was 18 1/2 weeks old as well. I have more than one Plymouth Rock laying now, but have gotten 4 no-shell eggs:/ Anyone else have the same problem? Today my smallest, but most developed leghorn laid her egg and I actually got to hear the egg song and it was quite interesting how the other hens and the rooster all joined in the egg song. I think the only reason that I actually got to hear the egg song was due to my 11 yr old accidentally locking me in the chicken coop, at least I thought it was an accident:/