To early to tell. What makes you think that they aren't pullets if that's what they are suppose to be? Did you get them from a hatchery? Most hatchery do a pretty good job of giving you the sex of chicks you asked for.
I have about 10 BA chicks that should be 23 or 24 days old. Some are chest-bumping and have nearly 1" tails so I figure they are roos. Others have much less tail and I see no chest-bumping. I did raise some BA's last year, and if memory serves, which I won't vouch for, this turned out to be correct.
Yours looks a little younger than mine. Maybe in a few days???