MegF.
That's for sale???
It's always great when they get going...however, you want to get on track for his age means you'd need to make him fat if you want the "average" weight...whatever that is. There is no on track for their age. Every snake is unique and each one develops at a different rate. My green tree python baby that was difficult to start (and I mean tough) is very small for it's age, but I expect that and won't feed more...just feed what I feed and it will eventually get there. My snakes mature slowly anyway due to a more conservative feeding schedule but they are all generally very active (except the eyelash viper...he just likes to sit there) and moving about all the time.