Well my leghorn started at 8 weeks, sounded like he was choking to death then a nice loud cock-a-doodle-doo! lol. Leghorns start early, I say with your breeds if you get a Roo, then maybe around 12 weeks or so...
Well Feed store people don't really "help" on breeds sometimes. I was told my Australorps were barred rocks when I bought them, I was suspicious with the white faces and didn't believe the feed store guy but bought them anyway because of the cute fluffy-ness! The friendly people here on BYC...
They are all looking like pullets so far, but you may want to wait another week or two. If you notice comb size changes are more red in one of them, then you may want to keep an eye on that one.