under age

under age

Below the age of majority—that is, not old enough by law to vote, marry, or sign legal agreements without one's parents. Typically refers to being under the age of 18, the age of majority in the United States, or 21, the age at which one may legally purchase alcohol. Spelled as a single word if used before a noun. He was sentenced to five years in prison for dating a girl who was under age. Bars caught serving underage college students risk losing their liquor license.
See also: age
Farlex Dictionary of Idioms.

under age

see under of age.
See also: age
The American Heritage® Dictionary of Idioms by Christine Ammer.

under age

not yet adult according to the law.
See also: age
Farlex Partner Idioms Dictionary

ˌunder ˈage

not yet an adult according to the law: We don’t serve alcohol to teenagers who are under age/to under-age teenagers.
See also: age
Farlex Partner Idioms Dictionary
See also:
  • below the belt
  • take the Browns to the Super Bowl
  • joke is on
  • do a Melba
  • for the long haul
  • blot (one's) copy book
  • blot your copybook
  • copybook
  • Barkis is willin'
  • below the belt, hit