Most of the people I know have someone over to a house around once a month or so, or do an event of some kind (gallery showing, horse trials etc) for similar purposes.
Age seems to have nothing to do with it. My said neighbors are uni students, I'm in my late 30's, my other neighbors are in their late 50's, and we've all been known to keep the block awake all night. No one complains, especially considering that friendly pre-party warnings / invitations are usually letter-box-dropped, and the late parties are usually confined to Friday / Saturday nights.
I personally love the house party vibe where I live. We may not all share the same music tastes, but it does my soul good to hear people having a good time pretty much every weekend!
It's possible that the reasons given in other comments (increased rent prices, social media redefining relationships etc.) are valid in Sydney as a whole, but thankfully they're having little effect in my surrounding area!
[1]: https://en.wikipedia.org/wiki/Newtown,_New_South_Wales#Cultu...
There's also a lot of the 'meet around 9-10, have some drinks, light food and music at home until about 11:30 when you turn down the noise, all bike/taxi to the city centre and start hitting some pubs around midnight and stay there until the clubs fill up with people around 1:30 or so and stay until 4, maybe club-hop inbetween and then all go your own way home. The house party is more of a place to meet collectively, to get some drinks in 5x cheaper than in a club and talk to people while still sober and in a relatively quiet place, a pre-party really.
By the 30s nobody really hits the clubs anymore (at 24 I've pretty much stopped already), plenty of parties at home though but usually there's no dancing involved which may tell you something about the nature of the party.