I have had several different types of layers all my standards have started laying near the 6 month mark. Those were: Rirs, californias, wyandotts, barred rocks, red dorking, Marans, White rocks, Sexlinks-black and red, Australorps, Buttercups. Of those birds they all laid either a medium egg or large, with the exception of the Buttercups they laid a small egg. I didn't like the Barred rocks but they were ok as far as laying goes. I have decided for my layers flock I am going to have a small flock of Rirs and Australorps. Mostly because of desposition. For me I like how the tempraments of the Rirs and lorps get along. Lorps lay in winter and so I won't have to buy eggs then. I want a 8 hen Lorp flock with roo and at least that many rirs maybe more of those cause I have no trouble getting rid of the hens. I prefer to sell off my hens at the start of their third year. They do lay well but I am always hatching.
In bantams: I don't think it matters what breed you have there mine all started laying at around 5 months. I never watched those as closely.
Arklady