Usually we say: "I am 5 year-old" (often when we talk about children)
"I am 20 years-old (often when we talk about adults)
Please could you tell me what's the difference, since the number 5 is plural why don't we say 5 years, instead of 5 year.
Just a note: A five-year-old child would get hyphens. (So would a fifty-year-old man.) The words with the hyphens work together to describe "child."
I'm not a teacher, but I write for a living. Please don't ask me about 2nd conditionals, but I'm a safe bet for what reads well in (American) English.
Karima, please see the Similar Threads at the bottom of the page.