Wow, really cool! I'm a big fan of Aussie pythons and am quite jealous right now...

All i know is that they stay pretty small and grow quickly so it could be quite hard to estimate the age, I can ask a friend who owns them if there's anything else you can do. From my experience you can expect a outgoing, fun, aggressive eater with tons of personality!

The aggressiveness you see in the cage could very likely be a feeding response which i have seen a lot from these guys. just pick him up from where he's not focusing and if i am right, he will chill right out.

Congrats!