Good morning Solomon,
You don't HAVE to be an Australian citizen to join the RAAF, but it helps...
As Dazza has implied, if you do the research, (and getting names right is rule #1 in any career) and if you show your recruiter you're taking the steps to get citizenship, it'll get your foot in the recruiter's door. Then as KC said, you'll still have to put in some serious effort to cross between wanting and getting, no matter which country you choose to serve. There's a lot of other young Wanna-bes out there competing with you. But it can be done, Solomon. So if it's really what you want, then go for it Young Fellah. Do the hard yards, and be a winner...