You are a US citizen, regardless where you live. And yes, US taxes all US citizens, legal permanent residents, temporary residents working in US, and other "US persons" as defined in law. US taxes ALL income from all sources worldwide, regardless where you live.
There is a double-taxation agreement with Australia, so your Australian taxes paid are credited against what you owe US. There is also Foreign Earned Income Exclusion for Americans living abroad, but it only applies to earnings from your job, not other income (like interest on bank account, rental income, etc.). You might not have to pay anything, but you still MUST file.
Your mom forgot to tell you that she put you firmly in the US Tax Trap. If you do not file annual income tax returns & pay as required, you are committing felonies. Also, US citizens (etc.) who meet certain criteria are required to file annual reports of all foreign bank & financial accounts (now FinCEN form 114), and/or Form 8938 for foreign assets. Failure to file these on time as required have truly draconian penalties.
Which is why the Australian bank has to report accounts held by Americans - and foreign banks don't want to have to comply with US laws in their own country. Which is why so many banks around the world now refuse to open any bank/financial account for Americans, including dual-nationals.
IRS is on the lookout for US dual-nationals who reside elsewhere - they want your money. And it is not uncommon to arrive in US to find IRS has a warrant out for tax evasion/tax fraud. So do not attempt to enter US until you solve your US tax issues.
Mom was supposed to get you a Social Security card when you were born & she got you your US passport. She needed that SSN to prepare her own US tax returns every year! So you both could be in serious trouble.
IF you decide to renounce your US citizenship, you must prove you have filed & paid your US taxes, and you may be subject to the Exit Tax - 42% of total worldwide assets. So the sooner you renounce - before you are old enough to start working, or have any savings, investments, assets, etc. - the better if you want to get out of the Tax Trap. Or do you plan to come to US, go to school, live in US, whatever, in the future?