I'm having the same problem with my hen/rooster. Can't tell which it is. I purchased what I thought were 4 pullets. All are about 20 weeks old now. This week one of them has started "crowing" if you can call it that.
I have a hen that looks just like that. I would have thought it was a roo until I saw it lay an egg!
Slender legs, shape of the body, lack of droopy tail feathers (don't the roos have long green ones in RIRs? Can you tell I don't have a RIR roo?
) all say hen to me.
One way you can check is to see how far apart the pelvic bones are. A roo will have a tight space between the bones - barely pinky-finger width. A pullet that is just about to lay will have a 2-3 finger-width space between the tips of the pelvic bones.