It really could be a big range, but average, Male: 12 - 18 pounds, Female:15 - 20 pounds. How they're fed when they're young has a huge effect on this sort of thing. If it weighs less than these numbers, it doesn't neccesarily mean anything bad.

Some Retics grow so fast that their length increases much faster than their girth, but their girth will catch up.

Email me if you have more specific questions.