Heya Baku. I wanted to reply to you as well just to say I fully agree with this system being really fucked up. I want to add some context though, because you’re incorrect that the legal definition of adulthood is just about being 18 in Australia. Gonna chuck these in bullet points:

At 16 you can become emancipated from your parents if it is unreasonable for you to live at home. You can then access Youth Allowance payments, as well as sign tenancy agreements.
The age of consent in most states is 16, otherwise 17. However, it’s still prohibited for people in positions of power over you, eg a Teacher or a Boss, until you’re 18.
Most states allow you to get your license at 17.
Once you turn 14, Medicare can’t tell your parents details of your medical treatments.
Once you turn 15 you can get your own Medicare card.
If you’re under 18, as long as you understand the advice and treatments, you have full control and consent over sexual health matters. This includes abortion & contraception, as well as things like PrEP (HIV prevention medication).

Edit: I forgot to add the point I was trying to make. The wage differences are even more fucked up when you consider there’s 16 year olds, being paid 60%, that have rent to pay. Our rules also make it a lot easier for people that age to escape abusive home situations, so it’s much more common even if the US has emancipation laws as well.