There is no guidline for a snake's growth. Too many variables to even consider this. If you own the snake and it's a fussy eater, it's going to be lighter than if it pounds a rodent every 4-5 days. If it was born light, it's got a lot of eating to catch up too.
Thre is a thread here somewhere about a lightweight hatchling. He was extremely light, but the breeder kept feeding him and he is now a respectable weight.
Good Luck!
Jim Smith