I hear you. I thought American university students drank a lot, legally and illegally. Then I went to study abroad in London for a semester, and made a lot of English friends.
Well, now. Compared to my friends in the UK, I was a consumption amateur. Even though for a time it seemed like I was subsisting on lager, I had to work to keep up during pub crawls. And my entire ancestry originates in the UK, so it was all cultural not genetic!
We're more trained, that's all. In Germany you can legally start at 16 with beer and wine, and the hard stuff is available at 18. Both in ordinary supermarkets, gas stations, wherever - the only thing that's forbidden is automated vending machines.
Compared to the US where the age limit is 21 in many places, well that's 5 years of drinking practice aka alcohol tolerance...
Well, ok. I can only speak for my side of the ocean, and not very authoritatively at that. :) Is it really widespread, though, for people in Europe to start seriously drinking before 16?
Naaaah.