In my untrained opinion, RIRs are tough to say as adolescents, because the pullets have so much of the same coloration as the cockerels, they're big, robust birds, and more "comb-y" than some other breeds. I have a RIR and she's surprisingly roo-ish in appearance and demeanor. Not quite confident as some roos, but certainly more confident than those I have of other breeds.
I don't think you can compare just TWO of them in your pictures and say for sure one is a pullet and one is a roo. If there was a flock of 10 or so, all the same age, and your suspect was the ONLY one with a comb that grown, then yah... but my pullet looked very similar to that at that age. Kinda worried me, too.
Can you wait a few weeks to be sure??