I don't think the not eating for 6 months affected his growth potential. I had a Rose Queen FH that went through that same stage at around 7-8" and did not eat a thing for roughly five months, lost his hump, stomach, and almost looked like a red terror in shape. Once I finally got him to eat it took quite a while before he gained back all that fat, but he eventually pushed 12-13"and roughly 3 pounds I'd post a picture but I don't want to clutter your thread with other fish.
Where you are feeding him only once evry other day it will increase the time to achieve his limits. I know he's 2 years old now but that is young for a fish like this. I can see you are attached to it and so was I to mine. He used to think that 6ft around the tank was his space and would ram the glass if you ventured in. But what a wet pet they are