I have to agree with Ryan, though I'd probably not say 100%, only because Ive had one pullet who was almost that light. Still, she didn't have that comb on her. I never say 100% because there's always that one that doesn't follow the rules of BR sexing. Here are two 12 week old BR pullets:
I see pullet...and I see cockerel. BUT...I'm going with cockerel based on the comb development and on the light barring.
A female should still have a pale face, comb and wattle at this age. There should be some pointy feathers coming in fairly soon. I "think" I see some already, but the neck is all "blurry" for me.
It's too early for that, really. I have a 16 week old cockerel who hasn't displayed any rooster-like behavior, either. BR pullets are rarely that light and I also think I see the stringy hackles coming in, like mikarod.
I have some Barred rock pullets and a couple Cuckoo marans, roos and females, I would have to say that My opinion is Roo, based on same deductions as Speckledhen.