Looks like a late maturing cockerel to me, them purebred Amer boys can keep you guessing for a while(been breeding them for 10 yrs and every year there are a few tricky ones).
When you check on his back/saddle area, part the feathers and see if the new pin feathers(usually still hidden under the old plumage) have blunt tipped feathers or lacy edged somewhat-pointy ones growing out.
Where did you get your Ameraucana from? If it's a feed store purchase then it's not an Ameraucana. Birds labeled Ameraucana's from hatcheries, which is where the majority of feed store birds come from, are always mixes and not actually Ameraucanas. They are called Easter Eggers.
@KBreedlove I was reading this post now as I have Easter Eggers that are difficult to tell also. I was wondering what the outcome of Roo Watch was. Did the feather trick work?