There are at least 3 major factors that can affect a BPs growth rate.
1) - individual tendencies, basically the rate the snake "should" grow at if it is offered sufficient food and remains healthy
2) - how much food it eats, obviously a picky eater or one that just isn't offered enough food is going to grow considerably slower
3) - parasites or illness that might slow down growth
Also, these things all affect each other, for example part of why a BP might appear to be a picky eater is it is just programmed for slow growth, so it can't make use of all the food you are offering it.
I'm going to make some guesses based on the weights of my snakes, but I still have a pretty small number so it isn't the best comparison. But I'd say the 100g, even if a late '08, is probably behind the average weight for his age. The 700g could be either a small '07, or a fast growing '08.