English Language Learners Stack Exchange is a question and answer site for speakers of other languages learning English. It only takes a minute to sign up.
Sign up to join this community
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?
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.
adjective
> (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.
