Depends on the tang. I have a powder blue and a naso. The naso is definitely growing a lot faster. I can see it growing 5 - 6" in a year. The powder blue not so much. I think the larger the adult size, the faster it grows. They also grow a lot faster when really small and as they get big, they slow down a little.
Yeah, all my fish are fat. In fact I started to put them on a diet lately.