I got an at-least-a-year-old BP from an ad on craigslist, from a girl who couldn't keep him. She had had him for 9 months, and of course he was at least 3 months old when she got him from Petco, and who knows how long he had been there! Anyway, he weighed 100 grams when I got him. . .I went straight to the privately owned pet shop to get some frozen rat pups and the snake guy refused to believe that he was a year old because he was selling hatchlings bigger than that. But why would she lie? Plus his tank was dirty enough to not have been cleaned for 9 months .

I think he was just underfed. So the same for your guy. I've had Leonard for a year and he's about 800 grams now. He's not a very consistent eater; he could be even bigger if he'd eat every week. So your guy will catch up too. It's a good sign that he ate for you so soon. Just keep up with the 10%-15% feedings every 5-7 days and he'll be fine.