If he's letting you rub his back in the cage at that size, you're off to a good start.

I acquired one in '91 at about 18" TL, and was a nervous wreck. Regurged, took off running, etc. Took a year and a half to calm down. Turned into a 6 foot awesome animal. Best lizard I ever owned. And I've owned quite a few...

Good luck with him. I just hope you realize it's not a big snake with legs...

Chris