Sounds comparable to mine. In a year from ~5" to ~12".
Mine, I'd say, is a poor eater. Only takes catfish farm pellets and even those not that many, maybe up to 5, and not that often, maybe several times a week, although I feed the tank twice a day every day. I've never seen it take a piece of fish, which I offer 2-3 times a week.
It used to eat a lot more, many pellets each feeding. In the past 6 months, it became as I have just described.
I know mine is not as happy as it could have been but it's a jerk and for now is confined to the jerk tank with the rest of them. 240 gal. Its nemesis is an 18" purple labeo.