Yeah, when I was on exchange, I wasn't "legal" to drink in the country I lived, but a lot of my friends where 18 and could buy mild alcohol in the shops (<20% alcohol) or any drink in a place that served food (20 was the age where can buy any drink, anywhere). We could have been sent home if caught, but people rarely were I think. I don't think they were normally shopped by their host families. But it was a situation where our exchange org didn't want to have to deal with everything associated with that sort of thing, legal or not. We couldn't drive either.
I don't know what I think about under age drinking. I did a lot of it, and seemed to get it out of my system. I am a very moderate drinker now. However, I know that it hasn't always worked that way here, and there's a lot of questioning about attitudes towards under-age drinking might be priming people for drinking problems. Maybe I turned out the way I was because my parents were basically teetotallers. I can count on my hands the number of times I've seem my mother drink, and she was drunk only once in my presence. My dad gave up drinking when I was 6. I don't think that my sort of environment is the norm here. But when I did start drinking, I sort of went crazy about it, and grew out of it.
However, in the States, the idea that people should get up in your business about drinking is awful. It's gotten to the point where pregnant women are told they shouldn't be in bars even if they are drinking soft drinks. WTF? I am not a proponent of pregnant women drinking, and I am aware of FAS and the horrors, but I also think the sort of paternal legal and social pressures in the States regarding it is a step or two too far. Then again, the first time I saw an obviously pregnant woman drinking here, I was a bit shocked, not only by her drinking, but that no one else seemed to bat an eyelid about it.