I have 4 barred rocks (at least I think they are BR's) and 2 black stars. I just bought a 50lb bag of starter/grower...still unopened... My friend just told me this morning she already put her 13 weekers on layer pellets. She said her other chickens began laying at 16 weeks last year. Should I go ahead and switch mine over? I thought it was a bit too early? Also when would I start the oyster shell? Once they begin laying?