You are 18, so you are legally now an adult, and are allowed to do anything you want within the law. Though you will need some kind of green card to get into Thailand to live. An alternative could be 6 months in Thailand, 6 months in Brisbane every year but that would get very very annoying. I know a girl who does that though.
Can I visit Thailand with my 19 years old son as my Travel Companion
Get on a plane.