about 18 years old
In the United States, all but two states require a couple be age 18 in order to marry without parental consent. Nebraska sets the age at 19 and Mississippi at 21 at the time of this writing (May 2003). A few states will waive this requirement if there is a pregnancy involved, but the couple may still have to have court approval.
Younger marriages require parental approval and a waiver. The minimum age varies per state most being 15-16...New Hampshire is the lowest with female requirement 13 and the male 14