When to move tanks?

Hi everyone!

Our little ball, Acheron, is almost a year old, about 2 feet long, and about the circumference of a half dollar. He is surprisingly active for a ball in our experience (we used to have two that we had to give away because of a lease term at the apartment we used to live in, and they were much more docile), and is usually crawling around during the day and at night, frequently trying to get out! He loves to climb branches and enjoys being handled too. He is definitely not the type of ball that usually stays in his hides. Anyway ...

We have him in a 15 gallon right now, and were wondering when it would be appropriate to move him into a 30. I don't want to move him too early because I know it causes them stress and they can stop eating. However since he is so active and crawls around a lot, I don't want to limit him by keeping him in the 15. Does anyone have any suggestions as to when (size / age / etc.) we should move him to the 30 gallon? We don't have much experience with snakes - we only had the first two for a year or so and we've only had him since October. So any help would be appreciated!

Thank you!

If it were me id keep him in the 15 as long as your able to properly maintain your temps, and humidity. your ball will be perfectly happy in that size enclosure for a long time. I kept my first ball in a 20 long tank and with my last 2 balls i made the switch to a rack and ill never go back.

I'm a rack user also, but if you are going to go up in size I'd go to a 20 long.
You can do that any time, contrary to popular opinion they do not NEED to be in a tiny environment.
Just make sure to add several hides, some fake vines and or branches and all the other tricks it takes to making a tank suitable for a ball python.