A lot of people get confused about when to use hyphens when writing ages, and I think it’s because sometimes an age is a noun, sometimes an age is an adjective that comes before a noun and modifies it, and sometimes an age is an adjective that comes after a noun.
When to Hyphenate Ages
First we’ll talk about when you do hyphenate an age: You do it when the age is acting like a noun and when the age is an adjective that comes before the noun and modifies the noun.
In this example, the age—70-year-old—is used as a noun, and you hyphenate it:
- That 70-year-old with a purple hoodie loves Justin Bieber.
Just as you’d say, “That woman with the purple hoodie loves Justin Bieber,” with “woman” as the noun, the age—70-year-old—can take the place of “woman.” When an age is a noun like that, you hyphenate it.
Here’s an example of an age that comes before the noun it modifies. You hyphenate here too:
- My 8-year-old neighbor wrote a poem about commas for National Grammar Day.
In that example, “8-year-old” is an adjective that describes the noun, “neighbor.”
When to Not Hyphenate Ages
Now we’ll move on to when you don’t hyphenate ages: When the age is part of an adjective phrase after the noun, you don’t hyphenate it. For example,
- Beyoncé is 37 years old.
- John’s twin sons are nearly 2 years old.
Neither of those ages are hyphenated.
So to sum up, you hyphenate an age when it’s a noun or when it’s a modifier that comes before a noun.
The main time you don’t hyphenate an age is when it comes after the noun it modifies.
Ages are like every other compound modifier that way: you hyphenate them before the noun but not after the noun.
[Note: Chicago style and AP style differ when it comes to ages. Chicago style is to use the word for ages 100 and lower, and AP style is to always use the numeral for ages. Our site uses a modified version of AP style, which is why the example reads “8-year-old” instead of “eight-year-old.”]