Writing Tip 71: “#-year-old” vs. “# year old” (a.k.a. “What’s up with the hyphens?”)
Remembering how old you are is one thing. Remembering where to put (or not put) the hyphens when you describe your age is another.
A thirty-one-year-old woman should be able to write grammatically. I am thirty-one years old. A thirty-one-year-old is old enough to know better.
Did you see those hyphens (or lack thereof)? They’re all correct. Do you know why?
Here’s the reminder: if the age is being used as an adjective or as a noun (as it is in my first and third examples), use hyphens; if the age is part of the adjective phrase following the noun (as it is in my second example), don’t use hyphens. Got it?
When a child is two years old, he or she doesn’t care about grammar. Maybe a ninety-year-old still doesn’t. Either way, knowing the rule doesn’t hurt, right?