18 Years Old or 18-Years-Old? When to Hyphenate Years Old

When should you hyphenate the phrase years old? Is someone 18 years old or 18-years-old?

In this post, I want to give you some advice on dealing with age in your writing. How should you write ages? When should you hyphenate? Should you spell out the numbers or use numerals?

After reading this post, you won’t ever have to wonder again.

Year old or Year-old?

The basic rule is,

  • Use hyphens for ages expressed as adjectives before a noun or as substitutes for a noun.
  • Do not use hyphens when you are simply stating the age of something.

years old or year old differenceIn other words, you want to follow a pattern similar to this,

  • John is 16.
  • John is 16 years old.
  • John is a 16-year-old.
  • John is a 16-year-old boy.
  • Arizona was roundly criticized when they acquired Segura during the offseason for a package headlined by Chase Anderson, a 28-year-old with a 4.18 ERA in 267 career Major League innings. –USA Today

In order to crystalize this concept, let’s look at a few more examples,

  • The 15-year-old boy won the race.
    • In this sentence, 15-year-old is acting as an adjective and describing boy.


  • The boy who won the race is 15 years old.
    • In this sentence, you are simple stating the boy’s age, so there is no need for hyphenation.
  • That is a 55-year-old bottle of whiskey.
    • Same concept here. 55-year-old is acting as an adjective and describing the bottle.


  • That bottle of whiskey is 55 years old.
    • You are simple stating the age of the whiskey. No hyphenation needed.
  • This is a birthday party for 10-year-olds.
    • In this example, 10-year-olds is acting as a substitute for a noun, so we hyphenate it.


  • The kids at this birthday party are all 10 years old.
    • Here, you are stating the age of the kids at the party.

More Examples

  • I am 21 years old.


  • I am 21-years-old.
  • I am 21 year old.
  • She is 20 years old.


  • She is 20-years-old.
  • She is 20 year old.

Trick to Remember Which to Use: Years old or Years-Old?

twenty one year oldI gave a lot of examples above to really drive the point home, but there is also a good trick you can use to remind yourself when to hyphenate years old and when not to hyphenate it.

A good trick is to look after the phrase. If a noun comes after years old, you will want to hyphenate it. For example,

  • That is a 25-year-old game.

Here, the noun game comes after year old, so we want to hyphenate it. But, if we rearranged the sentence,

  • That game is 25 years old.

When we rearrange the sentence, we do not need a hyphen because there is no noun coming after our phrase years old.

Should I Spell Out Ages?

16 year old or 16 years oldAP Style holds, as do many other popular style guides, that when writing the age of something in text, you should always use figures.

Do not spell out the age. For example,

  • She is 19 years old.


  • She is nineteen years old.

This same rule applies for children under 10 years old.

  • My baby just turned 2 years old.
  • He is a 2-year-old child.
  • Andrew’s 3-year-old sister, Lea, and his 5-year-old brother, Wills, were tested, and in the family’s first bit of luck since the diagnosis, Wills turned out to be a perfect donor match. –The New York Times

It’s easy to see why this rule makes sense. It’s easier on the reader and it doesn’t clutter up your text. For example, which of the following is easier to read?

  • We are celebrating the 150-year anniversary of our city.
  • We are celebrating the one hundred and fifty year anniversary of our city.

Using figures frees up your text of these superfluous words and makes it much easier on the reader.

Should I Put an Apostrophe in Years?

If you are saying that someone is in his or her 20s or 30s, you do not need to use an apostrophe. For example,

  • That club is primarily for people in their late 20s.


  • That club is primarily for people in their late 20’s.

The same goes for calendar years.

  • I was born in the 1980s.


  • I was born in the 1980’s.

Numbers and the Suspended Hyphen

The last thing I want to cover in this post is the suspended hyphen.

A suspended hyphen is used when you have two or more hyphenated phrases that end the same way. In situations like this, you can use the hyphen after the first word or phrase and “suspend” the rest of the phrase until the second one. For example,

  • The kindergarten class has both 4- and 5-year-olds as students.
  • This bar is full of 21- and 22-year-olds.
  • I had dinner with my brother- and sister-in-law.

Summary: When to Hyphenate Year Old

In this post we covered when it’s appropriate to hyphenate year old. Should you use a year old hyphen or not? Here’s the rule,

  • Hyphenate when expressing ages as adjectives before a noun or as substitutes for a noun.
    • The 21-year-old woman gave a presentation.
  • Do not hyphenate when simple stating the age of something or someone.
    • He is 26 years old.

Also, you always want to use figures when discussing age; never spell out the full word.

  • A 10-year-old boy.


  • A ten-year-old boy.