Huh? Unless I'm not understanding what you're saying, they're not determined by individual states <EDIT: This bit is incorrect>. The drinking age in Australia is 18 <EDIT: While the drinking age is set by each state or territory, it still stands that the drinking age in Australia is effectively 18 (in public venues, blah, blah, blah) since all states/territories have set it as such>.

Each state and territory has additional rules and regulations regarding who can consume alcohol but this is usually based on agreements or "accords", but not always.

Examples:

In the Pilbara, Western Australia many of the mining towns have restricitons on what types of alcohol can be purchased and when (no shots, no doubles, no take away beer in bottles over 750 ml, etc).

In the Northern Territory often only light and midstrength beers are available and often only to tourists.

On Groote Eyelandt, alcohol is only available to people who have a permit issued by the police and, generally speaking, you have to be a non-aboriginal to get a permit.

The drinking age still remains 18 in every state, however.