When I was fifteen, I left home and was made a ward of the state. In effect, this meant that no one was supervising me, or really ever would again. It was 1981, and my rule was simple: if you could get away with it, you should. This meant, of course, one had to experiment a lot to see what was possible.
Applying this rule, I figured if I could get into a club, it meant I was old enough.
My moral life has developed a bit since then, but in many ways, this still the basic gist.