There is a sentence like the following.

She is 5 years old

The part of speech of "years" is a noun, and after a noun an adjective "old" is placed in the sentence. Is the word order correct? Generally, an noun stands after an adjective modifying in a phrase. In the above sentence, what function does "5 years" have? Is "5 years" an adverb?

2 Answers 2


"Years" is unit. It is a special class of noun that can combine with numerals to form phrases like "three metres" or "six pounds"

These phrases may be used as modifier of an appropriate adjective. But there is a good deal of idiom. This structure works with length, time and age. Some similar expressions are not usually acceptable.

  • five years old (okay)
  • three metres long (okay)
  • six feet tall (okay)
  • forty-two years young (only to be funny)
  • twenty kilograms heavy (not acceptable)
  • two hours long (okay)
  • forty-five miles-per-hour fast (not acceptable)
  • 5
    Once again ELL has me nodding along then breaks my mind with obvious exceptions that I simply can't explain. And I'm a native English speaker. Jan 31, 2022 at 13:44
  • 2
    The last one would be fine if it was describing a class of fast. "This thing is fast. Like, thousand miles an hour fast."
    – corsiKa
    Jan 31, 2022 at 18:53
  • 2
    @corsiKa That's a compound adjective (should be "Like, thousand-miles-an-hour fast") and doesn't have much to do with units. You could also say "That guy is conservative. Like, Ronald-Regan conservative." or "That movie is funny. Like, rolling-on-the-ground funny." Jan 31, 2022 at 19:44

"five years" is called a phrase of measurement or a measure phrase, and it is normal to put these before an adjective that describes what they measure.

He is six feet tall.


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