What to invest in with a small income?

I'm a 14 year old with a small tutoring job and getting paid $300/month (AUD), my parents have a Stake account (both US stocks and ASX) and they have allowed me to spend my own money on it.

I've done some research and what I've currently got is that at my age, I should be looking at more long tern stocks (ETFs, Index funds, etc.). I was going to try putting some in the S&P500 to watch it grow and possibly retire early if planned out well.

However forex fees kind of kill my money when trying to put money in the US stocks account, so should I put it in an ASX ETF like VDHG, keep my initial plan of putting it into the S&P500, or just keep it in my savings account? Maybe even a mix of all 3?

Thanks 🙂