He really could be just a late bloomer. I LOVE roosters, so when I get one I watch them grow obsessively. I've noticed that mine seem to be slow to crow and mate, if I have a very dominant rooster or hen around them. I always considered it self preservation lol :D
I've had roosters who didn't grow decent saddle feathers until they were closer to two, and I have a sweetie at the moment who didn't get his until he was almost three years old :)