Five years old Five - years- old

five years old 正确
five-years-old 错误，当有连字符号时，要把s去掉。而且后面还要有名词。
如：She is a five-year-old girl.

Five years old 五岁 名词
Five - years- old 五岁的 形容词
He is five years old.他五岁。
He is a five-year-old boy.他是个五岁大的男孩。

I am five years old.
I am a five-year-old boy.

five years old 或者 five-year-old

前面的

中间不应该有 - 的。直接five years old