five-year=old和five years old用法有什么区别啊

前者用于名词前面修饰 后者相当于表语吧
例 he has a five-year-old son.
his son is five years old.

前者是附和名词作定语修饰另一个名词
如 He is a five-year-old boy.
特点是 加了连字符不加s

后者是系表结构里的表语
如 He is five years old
特点是 没有连字符要加s

一个是形容词：five-year-old ，并且year不能加s。

一个是短语：five years old ，这是year是个名词，要加上s。

英语中很多用hyphen隔开的词都是形容词。

没什么区别的

five-year = five years

five years old是名词
five-year-old是形容词