It will take time but you he will be another one to be proud of under your care. My small one is up to about 10". I've had him about 2 years and he was at least 6 - 10 months old when I got him.
I just this weekend found out you lost your big guy. VERY sorry to hear it. When you have had a fish for a long time and you are really proud of it, it really hurts when you lose them.
Mine is getting some eyesight problems. His left eye seems to be coming back but he can hardly see out of the right,.