In the United States, 18 is the age at which a citizen can enlist or be drafted into military service, marry without parental consent, leave the country without parental consent, and vote in governmental elections.
The original argument for raising the minimum legal drinking age is to lower the rate of drunk driving incidences. However, for teenagers and college students, the law simply leads to them drinking off-campus or away from their homes, leaving them to drive back inebriated. In countries in which the drinking age is 18, they maintain a lower incidence of drunk driving.
Choose Responsibiltiy, "FAQs," www.chooseresponsibility.org
Thomas S. Dee and William N. Evans, "Behavioral Policies and Teen Traffic Safety," American Economic Review, May 2001