Is There a Hyphen in “Year Old?”
Whether you should hyphenate “year old” is one of those little grammatical issues that isn’t really an issue at all. This phrase follows the same rules as other compound adjectives, which are two or more words linked with hyphens to show the phrase is part of the same adjective. Except, you know, for when they aren’t hyphenated.
Confused? Don’t be. The rule is straightforward.
“Year Old” as a Noun
If the phrase “year old” is used as a noun or comes before a noun, hyphenate it:
- My ten-year-old computer takes five minutes to boot up.
- That six-year-old paints like Jackson Pollock.
- A six-year-old doughnut is no longer edible.
“Year Old” as an Adjective
So far, so good. Sometimes, “years old” is used as an adjective phrase that follows the noun, in which case you don’t hyphenate anything. The phrase also becomes plural if the age of the person or object is plural: your computer is one year old, but your friend is thirty years old.
- My computer is ten years old and takes five minutes to boot up.
- Jim is one year old and paints like Jackson Pollack.
- That doughnut was six years old. I think I chipped a tooth trying to eat it.
Compound Adjectives and Phrases
As we noted, hyphenating or not hyphenating “year old” or “years old” is part of a larger grammatical rule governing compound adjectives. The same rule applies if you’re discussing two-seater airplanes, five-foot-tall men, or part-time security guards. For instance, when the compound is used as an adjective preceding a noun, you hyphenate:
- The two-seater airplane was small and uncomfortable.
- The five-foot-tall man had trouble seeing the stage at the concert.
- The part-time security guard didn’t notice the vandals.
You also hyphenate when the compound phrase is used as a noun:
- He flew the single-engine two-seater through a blizzard.
- Large for his age, the four-year-old was five feet tall.
You don’t, however, hyphenate when using a compound adjective as an adjective clause following the noun:
- The plane’s single engine couldn’t provide enough horsepower to lift the heavy payload.
- The man only stood five feet tall.
- The security guard only worked part time and didn’t want to risk his life confronting the vandals.