Why do some say:

After a child's second birthday, the rate of growth continues to slow. Two-year-olds are very active and begin to lose the appearance of a baby.

Two-year-olds, not, say, Two-year-old babies.

Why do we pluralise Two-year-old and make it a noun? Is this likely to be right or not?

  • 1
    We do the same thing for every age - ten-year-olds, sixteen-year-olds, etc.
    – stangdon
    Commented Jun 8, 2022 at 0:04
  • This isn't exactly what you're after, but it might be of some use.
    – user8719
    Commented Jun 8, 2022 at 4:28

2 Answers 2


In English it is common to take verbs and use them as nouns, to take nouns and use them as verbs, to use adjectives as either nouns or verbs, and vice versa.

In particular, phrases such as "two-year-old", "five-year-old", and "twelve-year-old" can be used either as adjectives ("twelve-year-old scotch") or as nouns ("you should see how my twelve-year-old has taken to music" or "She is the best two-year-old to enter the Derby in years.") The example sentence is simply a case where the writer has chosen to use a noun form rather than an adjective form.

Because using the noun form permits omitting a word ("baby", "child" or "horse"), it may be favored with the modern pressure for brevity.

two-year-old noun
> a person or animal that is two years old.
> (of a person, animal or thing) that is two years old.

See also Difference between "two years old and two-year-old"


In this the writer is generalising the "baby", so it is talking about all the babies on general and therefore plural is used and it becomes a noun. People only use singular when specifically referring to something or someone. So yes in this case using plural is perfectly fine.

  • I don't think this answers the question. I think the OP is asking why the text uses "two-year-old" as a noun, rather than as an adjective modifying "baby"., and in the prcess of using it as a noun, make it plural. Commented Jun 8, 2022 at 0:47
  • @DavidSiegel Oh thanks, but does "generalising" the term "two-year-old"/baby turn it into a noun, it works in this case I think
    – DialFrost
    Commented Jun 8, 2022 at 0:54
  • I wouldn't call it "generalizing" When a mother says "My two-year-old is just starting to walk.", she is not generalizing, she means "my two-year-old baby" not any other kind of being, it is no more general as a noun than as an adjective. When a noun is used as a verb we call it "verbing". We could call tis process "nouning" but no one does that I know of. We just call it "making a verb out of". " Commented Jun 8, 2022 at 15:17

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