2 year old vs 2 years old

English as a Second Language English Vocabulary, Grammar and Idioms
1

I know this topic has been covered on earlier forums but I have not found that the feedback has explained the reasons for the two forms.

Ben is a 4 year old.

Ben is 4 years old.

4 year old Ben…

Please help me with the why of the grammatical form.

Thanks

2

They’re supposed to be written like this:

“Ben is 4 years old.” (“Years” is a noun here, so it can be plural.)

“Ben is a 4-year-old.” (“4-year-old” originates as a compound adjective here, and the nouns inside a compound adjective usually can’t have a plural suffix.)

“4-year-old Ben…” (Ditto.)

3

Thanks Jamie :smiley: