At your age you need an AME apprenticeship. You have a number of apprenticeship options:
MEA40715 Aircraft Maintenance Engineer - Mechanical
MEA40615 Aircraft Maintenance Engineer - Avionics
MEA41315 Aircraft Maintenance Engineer - Structures
Contact your local Australian Apprenticeship Support Network (AASN) to find out which of those apprenticeships has a Registered Training Organisation (RTO) available in Darwin. It appears there is only one AASN in Darwin - Australian Apprenticeships NT, 38 Woods Street, Darwin, which is also a Group Training Organisation (GTO) who may be able to offer you an AME apprenticeship through one of their employers.
If they can't help you with an apprenticeship, you must help yourself by contacting every aircraft maintenance organisation and airline in Darwin/NT seeking an apprenticeship. The military is another apprenticeship option, although not in my opinion a first choice as most military aircraft engineering is now carried out by civilian contractors.
During your apprenticeship you will compile a Schedule of Experience (SOE I think it is still called?) which lists your various work experience competencies, signed off by your supervising LAME.
On successful completion of your four year apprenticeship, you sit the basic AME CASA licensing exams, provide your SOE to verify your work experience, and your whole new life of frustration in the aviation industry begins.
A word of warning: If you are not prepared to live on a low apprentice wage, want a flash car instead of a used bicycle, want a hectic social life, are not prepared to study, can't get out of bed in the morning, don't want to sweep the hangar floor or are a gentle petal that can't take a few straight words from your superiors, go seek a career with McDonald's, KFC or Hungry Jacks.
After decades in aviation and apprenticeships, I have little time for the 60% of Australian apprentices (60% and higher has been the apprentice failure rate for some years) who start their apprenticeship and never complete. It is they who are most vocal against the overseas 457 qualified workers who "come here and take our jobs", great career opportunities that a majority of Aussie kids no longer are prepared to work hard for.
Good luck!