'Twas a mouthful of beer when I was about 1 year old. I have it on video, actually.
They let me drink a bit of beer, and when they then removed the glass, I tried to crawl up on the table after it. Looks like I liked it; which is weird. You would think a kid couldn't stand beer.
Edit: The first time I drank any significant amount of alcohol though, was on a vacation where I asked if I could taste some of the ouzo. I was 14 at the time, I think. The ouzo was kept in a two liter bottle, you see, so they had a hard time dosing it correctly. Thus, I got more than they had intended.
I have of course tasted some different spirits before that; but only tasted.