Breed and egg color, most of the time if a chicken has white earlobes then they will lay white eggs. If they are red earlobes they can lay brown (or blue eggs if they have the blue egg gene) eggs. Also Leghorns have white earlobes so to be a Leghorn then you have to have white earlobes, they...
I would say they were at least 8 months (once they are laying it is hard to say how old they are). Do they have white earlobes? Some look like they do but some look like they don't.