I'm assuming GAP year is after year 12 before uni, pilot training or something else. In which case you will be 18-ish.
A gap year is a good thing to do. Australia is a good place to do it. Depending on what country you are in, it is easy to get a working VISA while you are young (under 25 I think, but I'm not sure).
I presume you want a job related to aviation because it interests you as a career and you want to learn more about the industry.
For someone young and unqualified seeking casual work, the typical things are going to be hospitality and rural / remote areas will be easier than the city. In an aviation environment I'm struggling to think where you'd fit. The airlines, etc are unlikely to take someone short term & foreign and the small companies are too tightly run to have someone who is not fully productive. Airside work will almost certainly need a security clearance which is likely to take 3 months (depending a little on your country).
I think you might be better to take the work you can get and mess around at airports on weekends. Someone else might have a better idea.