>>Go to ADFA (The Australian Defence Force Academy) and do computer science<<
First of all - G'day fellow Aussie!
This would be an excellent thing to do - not only would the Army pay your way through university, you will also start off as an officer, not just a grunt (not that there's anything wrong with that, but face it you'd wait years to get anywhere!).
Either way, really have a good think about it, and get in contact with ADFA to find out more.
At 14 I didn't even dare to think beyond the end of school. Even when I finished at age 17, I still had no idea what to do really. I was going to just go direct entry into the Army, but then I decided to do a 3-year Information Systems degree at uni instead. I'm glad I did, because there is no way I would have been ready for the pressures of ADFA. Having said that, if this is something you really want, I think you should go for it - just make sure you know all of your options before making any decisions just yet
Best of luck mate!