How fast do BP's grow?

I have a July 08 hatch pastel female who weighs barely 300 grams. She eats regularly (once a week, ft weaned rat) and never misses a meal, she just won't grow! I also have some other snakes that hatched around the same time as she did and they are in the 500+ g range. I have two late 08 (end of Nov) hatchlings, a normal and a mojave, that are about 200 grams now. So it all depends on the snake. I feed once a week usually, sometimes I'll go up to two weeks, but that's not common for me, especially with the little ones.