I'm probably not going to be a lot of help here but I'd like to learn the answer too.
I do Think that he will grow more, as I've read that they don't reach their full growth until around 2 yrs.
I have a rooster that has continued to grow. At 2 yrs he is bigger than I anticipated and I wish he were not so big for the sake of my mixed flock girls.
He is not a brahma, he is 1/2 blue orpington (breeder stock, I was told/ my hen hatched his egg) and 1/2 ameraucana. He has gained almost 1& 1/2 lb. Since his 1st birthday and has topped out..I hope at 12lbs.
He is a great rooster, but if I ever get another I'll find a smaller breed. He has produced some large offsprings..both pullets and cockrells.
He does best with big girls like orpingtons and langshan. He is a bit overwhelming to my smaller hens. I did buy him a few feed store brahma girls this spring. They are still in the brooder.
I love big chickens but my climate is hot in the summer and I like keeping smaller hens too so I feel that I should have gone with smaller breeds.
Hope someone else will chime in and answer your question.