Mostly, it will vary snake to snake. One might be a great eater while another - maybe even from the same clutch - will be picky, refuse, and grow at half the rate. From what I've seen of her, though, Buggsie is far from a picky eater. She's never turned down a meal, even when so blue no one could've blamed her.
I do know that of other snakes I have of the same age, the next smallest one is above 350. Which puts Buggsie considerably behind.
While certainly not written in stone, The Red Dragon Den has posted on their website a 30 month long informal study of growing Ball Pythons. The study includes an average weight for the animals used, plus individual charts. As you can tell from the individual charts, some were better eaters/growers than others. I will occasionally refer to the averages chart to get a general idea of how my balls are doing - are they growing fast? Are they growing slow? Are they right in line for average growth?
One thing to remember is that how they look is more important than their numbers. A snake that is on target for age, but looks overly fat is just as bad for the snake's health as a severely under fed one.