Hyphens, En Dashes, Em Dashes

Q. I can’t find hyphen placement in ages, such as “fourteen-years old” in the Manual. And what about “years-old”? Is that correct?

A. There is no need for hyphens in “fourteen years old.” If you are using a phrase like that to modify another word or phrase, however, you need to bind it together with hyphens (a fourteen-year-old grudge). Likewise, use a hyphen if “years old” comes before the noun it modifies (a years-old phobia over wearing the wrong earrings), but leave it open if it follows the noun (the moldy accretion on her cell phone was years old). Finally, you will need hyphens when the phrase is used as a noun (enough pizza for three fourteen-year-olds). Please see CMOS 7.85.