English for Today by Ganiu Abisoye Bamgbose (Dr GAB)
Qualifying Nouns
I saw a 40 years old man (nonstandard).
I saw a 40 year old man (standard). The ‘year’ will not attract an ‘s’ because it precedes another noun,man. This also applies to:
It’s a two days programme (nonstandard).
It’s a two day programme (standard).
The man is 40 year old (nonstandard).
The man is 40 years old (standard). In this case, ‘year’ is not preceding another noun so it should be pluralised.
GAB