I adopted my BP last year from his previous owner. He was almost 3 years old and weighed 375 grams. I have been feeding him one appropriate sized meal a week for the last year and he is now 750 grams.
His weight gain was significant for the first 9 months but he has tapered off now to being fed every 2 weeks. He will probably top out at 800 to 850 grams and that could be due to his previous owner or maybe he is just a small male. It’s hard to say in my case but your snake doesn’t sound like he was severely under weight.