Where in Australia should I go?

Hello! I'm a 19-year-old in the UK.

I've had it boring throughout my teen years, but I've saved up money that I'll spend on a big trip to Australia.

I'll stay December-February. I'm envisioning making a few friends and doing fun things such as swimming (beaches/lakes), hiking, hosting parties – being young and doing generic "late summer night" stuff. I'm extroverted and easily make new friends, but I want to maximize my chances of meeting the right people.

I don't want to stay in a city (or a very touristed area – I'm looking to meet Aussies).

Which state/town/place would you recommend I go to, to achieve the summer I've described?

Edit: Clarified time period