In places where it is cold and there's low population density, there's not much for teens to do to entertain themelves in winter but drink. Northern New England scores high, too. I had a friend from Vermont, he was as experienced a drinker at 18 as I was at 25.
I grew up in rural Ontario with a bunch of Mennonite boys. We were all regulars at the local bar when we were 18. And there were plenty of back roads and woodlots if we were looking for a place to knock back a few.