[ Other - Health ] Open Question : dangers of underage drinking?

I know that in other countries, kids can drink alcohol years before it is legal for an american kid to do so. If a kid that is 16 were to drink a beer (or a serving of any other alcoholic beverage) per day, what effects would ensue? are there any standout positive/negative effects to drinking before age 21 if it is in moderation? how would the effects vary on a 14 year old? on an 18 year old?

Source: http://answers.yahoo.com/question/index?qid=20110411215901AARwOiH

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