I have a barred rock, that look just like yours. Mine are 21 weeks, all have red large combs except for the one is lighter and small, but otherwise healthy. I just assumed she was slower to mature. I sure hope "she" is not a "he". Roos are not allowed here either. The comb looks like the others did in the beginning. I will post a picture later.
Oye! Of all the luck! Oh well. I guess we'll just be enjoying roaster chicken here pretty soon! But while we are assessing my little flock, maybe you can help me make sure my last bird isn't yet another rooster. Here's my RIR: