March 3rd 1986 was the date that the Australia Act took effect.
Prior to that, the Australian constitution was an Act of British Parliament we couldn’t change without the assent of the English House of Commons, and Australian High Court cases could be appealed to the British Privy Council.
So we weren’t in charge of our own constitution or our own court system. We weren’t independent from Britain in any meaningful way.
That changed with the passage of the Australia Act. Thirty nine years ago. That’s how old we are as an independent country.
March 3rd should be a public holiday marking our national Independence Day.
We choose to celebrate our formation as an English jail instead, and the main reason we do it is belligerent unselfconscious completely normalized racism against Indigenous Australians, baked into the very fabric of our colonist culture.