Take a look at your hens for comparison. Their necks feathers (hackle feathers) are nice and rounded like a lacey doily around their necks. The male's will not be rounded like that.
Oh, RIRs are pretty big. The females aren't quite as big as BO females, but they're not small either. My main...
I can't be sure, but she looks like my barnyard RIRs.
RIR boys usually get their big red combs pretty early. I can usually identify the boys by about 4 week because of their combs being so much bigger than the girls. If you can remember that, you might be able to say for sure.
For eggs or...
I'm not entirely sure on the gender (i'm thinking female); it has been a while since i saw a 14 week old - but are you sure the one on the left is a cross? My rirxbo babies are a terra cotta color. That one looks red to me.