I just picked up a couple ball pythons from Morphmarket from a big breeder who has sold over 1,000 snakes on that site. The pair was supposed to be over a year old and I didn't think the weights were accurate. Just unboxed them today and sure enough the male is only 166 grams!! I have hatchlings that are only two months old that weigh twice that. I'm guessing that they just didn't feed them or maybe a rat pup once a month? I was pretty shocked to see how light they were, it was like opening up an empty box, I thought maybe they forgot to put the snakes in there LOL.
I feed pretty heavy, at one year old most of my snakes are up to about 800 grams and usually at least 1200 grams after two years. I've had one snake this light (a normal that I got for free) and with heavy feeding she grew like a rocket and made up for it in no time so I'm not that worried about it, just thought I'd share my experience with this big breeder... (not going to mention any names).