I saw a tweet about hyphenation earlier this week, and I thought this would make a good grammar tip, because I have to correct this almost every time I edit anything with ages.
This is going to be short and sweet. (Note: these are just grammatical examples. I do not actually have a seven-year-old.)
Correct: I have a seven-year-old.
Correct: I have a seven-year-old daughter.
Incorrect: I have a seven year old.
Correct: My daughter is seven years old.
Incorrect: My daughter is seven-years-old.
Here’s the difference: One example is using age as a noun (seven-year-old); one is using age as an adjective phrase (seven years old).
When using age as an adjective before a noun to modify it OR when using age itself as a noun, use hyphens.
When using age as an adjective phrase after a noun, do not use hyphens.
Here are more examples:
That lady looks like she’s eighty years old, but she’s only twenty! <–adjective phrase after a noun
That twenty-year-old looks like she’s eighty. <–noun
The twenty-year-old lady looks like she’s eighty. <– adjective before a noun
I hope that helps! Feel free to leave any questions in the comments.