under the age of (a number)

Usually, when you compare someone's age to a number, you just say "under" or "over" like this:

You're not supposed to drink in the U.S. if you're under 21.

But in more formal writing or speaking, you can use the phrase "under the age of ___":

Persons under the age of 21 are prohibited from buying, consuming, or posessing alcoholic beverages.

This phrase appears in these lessons: