I will be 70 next month and have had over 35 occupations during my working life. (And still working BTW). The trouble is I let a 15 year old kid decide what I was going to do for the rest of my life without the wisdom of older people. At that age my father had opted out of family life and was dead two years later.
My first choice of occupation was to be a plumber but my mother said you don't want do that it's too dirty. So I picked an occupation off a list and didn't even know what it was about. Patternmaking something even my mother didn't know what it was so couldn't say one way or the other. Now a dying trade.
My advice is seek out advice from older people, do an aptitude test as some of the others have said go and do some work experience but by all means go to at least year 12 because by then you will be letting at least an 18 year old rather than a 16 year old making a rest of life decision and year 12 will give you many more options.
If you do decide to do a trade do a transportable one like electrician, plumber, fridge mechanic, motor or diesel mecahnic.