How can I voice my opinion as someone who is still too young to vote?

Now I reckon I know a lot more about what's going on politically than plenty of people who are over 18, but it seems as though there is nothing I can do to influence the direction of my country - especially considering conservative inaction on things like climate change which affect the world that my generation will be leading but is overlooked (mainly bu the libs) because they are too selfish to look past a few thousand annual boat people. How do the major parties ensure that they are looking at the wants and needs of all Australians, not just those old enough to legally express their opinions? And why is the voting age 18 when people my age are perfectly capable of having an opinion as well?