Eleven year old, eleven years old, eleven-year-old. Which one is the right one?

Hello, Guest.
If you want to focus on correctness, you might want to avoid using "eleven year old" (without the hyphens). The reason is that, if you use the three words separately, you need the plural "years" when you talk about "eleven".
On the other hand, it is correct to use the noun "year" -in singular- if you use hyphens.

1. She is eleven years old.
This has the same meaning as "She was born eleven years ago", and you wouldn't use "year", in singular, in that sentence. You are speaking of a certain number of years in both cases.

The following sentences are different:

2. She is an eleven-year-old girl. ("eleven-year-old" is an adjective)

3. Eleven-year-olds are noisy kids. ("eleven-year-olds" is a noun)

Miriam

The problem is very simple: you tried to "reconcile" my explanation with your sentence when your sentence does not exemplify my explanation. I provided examples for my explanations.

And I also mentioned focusing on "correctness", not on what is "more common". Sometimes what is more common is correct, some other times it isn't.
It is not possible to make one sensible post adding mine to yours; they are different, even opposite. Your sentences are not examples of the explanations I posted.

I didn't take my information from google or from "my" logic, but from grammar books. In general, I don't like to use search engines when it comes to grammar, I don't need them when I have information from grammarians. If I found a good grammar book online, written by an authority in the subject, and if it were a book I don't own, then I might use it, of course. But "hits" won't tell me much unless I carefully read each of them. So, since I don't have the time to read 10.000 hits, I'd rather stick to grammar books. I wouldn't tell any of my own students to rely on a number when I don't know what makes up that number. I personally prefer to post information I can account for.

You said that in my sentence #2 "eleven year old" might be used. I don't doubt some people might rewrite it in different ways, but my point was precisely that even when three separate words may be common in that example (which I honestly don't know), the hyphenated option is more correct.

When you use "year" together with other words to have a multi-word adjective, you use "year" in the singular, and that is why it is better to hyphenate the three words (unless you're saying "my son is one year old", in which the use of the singular is obvious), as in "an eleven-year-old kid".

My whole point was that when you use "eleven years old", in the above example, as three separate words, it is correct to use "years", in the plural, because that noun will be the head of the construction (a noun phrase). In other words, such a construction cannot take "year" (in the singular) as head and still be 100% correct: "eleven year old" lacks concord.

We say "The building has three storeys", but "that's a three-storey building". Notice the difference: when the noun (storey/s) is premodified by a cardinal number and both together, at the same time, premodify another noun, you hyphenate the first two to make a compound adjective and avoid ambiguity or awkwardness.


I don't doubt your question was sincere.
But let's hope that not everyone will misunderstand my explanation.

Miriam