After enlarging the pic of Joonie I'm almost thinking you may very well have a roo on your hands. On the other hand, she could just be asserting herself as the top chicken in the flock and letting the rest of them know it.
As for age, I really think these chickens are younger than 27-28 weeks which if they were that age would be around 7 months old. They don't "appear" to be filled out and looking like true adults just yet. But as some of your girls are doing the submissive squat just keep a keen eye out and you'll get that first egg when you least expect it!
