How often should 9-10 month old ball python be eating

[Bogertophis]

That's hard to answer without more information. Like without seeing the snake, to assess his current body condition. Snakes gain or lose weight based on their metabolism & on how much food is available to them. Their metabolism is based on temperatures they're kept at (assuming captive). As far as meals, some people feed prey that's too big, while others feed prey that's too small. So how can we tell you without knowing more & seeing him? A snake that's overfed is likely to refuse food- every 10 days* is a bit long for a young BP (under a year) unless his meals have been on the large side, in which case he's trying to tell you something. (*Though in the wild, it's unlikely they'd eat anywhere near that often- but they also have more variable temperatures too.)

As far as a snake being willing to eat, there are other factors too. For example, excessive handling is an appetite turn-off for snakes. As is an enclosure that doesn't provide enough "security" (proper hides for privacy, & proper temps. etc.) And if a snake is too cool (think about your use of A/C in summer, house may be cool?) that's another reason snakes may hesitate to eat, at least if they sense that. So double check temps. inside the enclosure- don't just go by what a thermostat is set to- that doesn't matter, it's what the snake is actually experiencing where they live.

Young snakes normally WANT to eat fairly often, as they're growing faster. If they don't want to eat, there's something wrong, either with the prey, their home, or perhaps handling.