In a majority of European countries and other places around the world, the legal drinking age is 18. While hard liquor often has stricter regulations, consuming beer and wine is common practice in these areas. This age limit teaches responsible drinking from a young age. Many American teenagers learn to drink in secret and with friends. This often leads to binge drinking and other harmful practices.
In addition, if an 18 year old can fight and die protecting the freedoms of this country as a soldier, he/she should, at the very least, be entitled to a beer.