Cockerel, sorry. 100% positive, no doubt about it. You can see the skinny saddles coming in now and it's cockerel-colored. It is slower developing, but I've had those. If that's a pullet, it's the only one with shiny, skinny saddle and hackle feathers I've ever seen.
Are you really positive about the age of that bird? Seems more like a 12-14 week old male to me.
Here is a 15 week old BR cockerel (it's Zane as a youngster) for comparison.
Boy, gonna be a big boy eventually. I just had a black rock steathily go from hen to pullet in about three weeks time - in the same age range darn bird. Suddenly when I stopped watching closely there cropped up all these darn pointy FEATHERS on his neck and butt. I'm ticked. Oh well, time to breed black rock to blue rock.