BA's and Leghorns can lay at 16 weeks. Some won't lay until after six months. Some don't lay until much later than that. If you had enough for averages to mean much you'd see some kind of regular curve where some start early and others start late. You don't, you only have four. That's not enough for averages to mean anything. More sh0uld start laying soon. I don't know which ones or how soon.