Austria, Brazil, Germany, and the UK region of Scotland (for devolved parliament and council elections only) have already enfranchised 16-year-olds. We should too.
There's currently a Parliamentary Inquiry into civics education, engagement, and participation in Australia. Changing the voting age is not in its terms of reference, but a large enough number of submissions calling for that could at least get a broader national conversation started.
(I also plan to put into my submission something about other voting systems and how feeling like your vote actually matters in a way that it largely doesn't in IRV would be a big help for civic engagement.)