I have 6 ISA Browns that turned 15 weeks old and the very next day one of them laid an egg!! I knew they were bred to produce early and a lot but that seems really early. 4 days 4 eggs - 2 were little but nice and 2 were soft. We haven't had an egg for the past 2 days, however they free range around the yard and it's possible she might be laying her egg somewhere else. I keep searching, like going on an egg hunt!! We are giving them layer feed now and extra calcium for their shells. This is our first experience with chickens so we are pretty excited!!