For a 20 year old rookie, I think he is doing outstanding. It is well known that bigs take longer to develop then perimeter players. Most of them aren't even drafted until they are 22 ffs. Even the great Dwight Howard only averaged 1.4 bpg when he was 20, and he was in his second year playing almost 37mpg.
With his work ethic and attitude, I see him as a beast in 3 years.