If you're talking strictly game design, good hobby. No way are you getting a job in Australia as just a designer.
If what you meant to say was "game development" then that depends on whether or not you plan to go to uni, you want to sacrifice having a decent income for several years, and you have the motivation to work on one project alone for several thousand hours.
Because you'll have to either move to the US (where you'll struggle to stand out without a degree) or start/join an independent developer in Australia which means having either very low or completely unreliable income (if you start your own you won't have any income until you finish something)
If you're interested in game development you should be looking into general software engineering, not games specifically. That way you can have a well paying job while exploring other options.