请问X-year-old和X years old 的区分和具体用法?

问题描述:

请问X-year-old和X years old 的区分和具体用法?
还有 X-year-olds

X-year-old
例子:She is an 8-year-old girl.
X years old
例子:She is 8 years old .
X-year-old可以算是一个形容词词组 其中注意要有短横 而且year不能加s.
应该是不存在X-year-olds这种结构的