My smallest '08 weighed that back in June. But he hatched in August '08.
So, that's 4 months. If that snake hatched in August or September '08, it's a little small. If it hatched in December, its weight is ok.
Just my opinion. If a snake IS a bit on the light side, there's only two likely possibilities--the owner isn't feeding it very much, or the snake doesn't eat well. Occasionally some snakes just grow more slowly.