I have a BO 'hen' that wasn't a hen. At about 4 weeks I began to notice the difference, and now at 5 weeks you can definately tell it's a roo. The comb is a little bigger than the girls', but the main way you can tell is because of the color. Talk about some BRIGHT red!!! There ain't no mistaking that one!!! I don't know what size a 9 wk old BO pullet's comb should be, but I know that just based on color I'd say pullet. I've also noticed that my BO's comb is larger all the way down its' head, not just in the middle like yours.
Edit: I think it's a hen