I think, sadly, that my first alcoholic drink may have been Warninks Advokaat - most probably because it was the one drink nobody wanted. It was ok actually, and I would have been around 13.
My first drink of the paid for type was Ben Truman at the Dolphin in Leighton Buzzard when I was 16. The Dolphin is now an old people's home but you could taste the hops in Ben Trumans, apparently.