I was under 10 when i had my first drink, but didnt regularly drink (1 or 2 drinks every 3 or 4 weeks) til i was about 13, which was when i was able to occasionally get served alcohol without ID at footy and cricket matches.
My parents were always relatively chilled about things when i was 14, as they knew i was able to buy alcohol myself more often than not, so by age 14 and 15 they were happy to buy me a 6 pack from time to time if i was going to a mates place or a party, the way they saw it was that if they bought it for me then atleast they knew what and how much i was drinking, and as a result i was always pretty honest about what i was doing and where i was going.
It was a good way to be, as i saw some people who had trouble getting alcohol when they were about 15, so when they finally were able to get it they made sure they made the most of it and got enough to last, this usually ended in them being pretty messy and finishing close to a whole bottle of Beam or something like that.
when i was 15 and abit, i was regularly able to gain entry to a number of pubs and clubs around Adelaide, and by 16 it was a majority, when i was 16 and abit, i could pretty much get into all pubs and clubs except for those with a reputation for being strict on ID.
Age 17 i had passed in what would have been over 50 licensed venues around Australia (Including some pretty interesting places in Kings Cross

), that was until i got busted in the Adelaide Casino underage, copped a warning and then had to sit it out til i was 18
When i turned 18 i went pretty hard for a month or 2, but then I found I was over it all abit, suppose i had just gotten out my system i guess.
Now Im 20 and I find I drink less, and less often than most other people my age, so i suppose in that sense getting fairly used to Alcohol under 18 is a good thing, particularly because generally once over 18 people have more money to spend on booze and its alot more freely available.