In Australia, 18 is the magic age. Your new life begins. At that age you can buy hitherto unavailable things, like pornographic films (of which I have none) and alcohol (of which I have spent...a decent amount on
). You can get into places like nightclubs and strip clubs (only nightclubs for me). You can also vote and stand for elections (I haven't done either), although you can join a political party at 16. You can get a learner driver licence at 16, and your provisional 1 licence at 17. At 18 you can get your provisional 2 licence, which you keep for around 2 years before you go for your full licence.
So yeah, everything pretty much revolves around being 18.