fifteen-year-old 和fifteen years old 有什么区别?包括他们各自的用法

Question

fifteen-year-old 和fifteen years old 有什么区别?包括他们各自的用法

Answer 1

fifteen-year-old 相当于一个形容词,修饰名词.
fifteen years old 是“数词+名词+形容词”结构.
比如：
He is a fifteen-year-old boy.= He is fifteen years old.