Mine are six months old and they're huge. I call them my fat-bottom girls. I dont' have any Brahma roos. I can't imagine how big they would be my Barred Rock is big enough!
My Light Brahmas from Cackle Hatchery seem to have much shorter legs than yours. I think yours are really pretty. I usually like the mixed breeds the best anyway. Lord knows I'm not perfect so I don't expect my chickens to be either.