The largest snake I would probably say you should get would be a BCI. I would never recommend you getting a retic, burmese, rock, green/yellow annie.

Focus on just this being a hobby for you for now, at 13 you're going to have limited help and time to take care of animals plus you shouldn't jump into something for the money. I've bred boas before and the market for them has gone down in recent years so I don't even deal with boas anymore, not because of the market but because of the more common breeding problems with boas versus pythons. It's because of live bearers vs laying eggs, different complications. Boas get larger, so require larger food which is more in the long run, but ball pythons have nit picky feeders at times.