My yearlings are all over the board. I have two smaller ones that are the same age as the others that are about 600 grams, and then I have several others that are over 1000 grams. It all depends on the snake. The smaller ones are kept in the same rack, so same conditions and are fed the same thing. The smaller ones are more likely to miss a week and are a bit more picky eaters.
I think some of it may also have to do with their locale (where they or their parents/grandparents) were collected.