这里的考点主要是14 years old 与14-year-old的区别
e.g.She is 14 years old.
She is a 14-year-old girl.
很明显14 years old作句子的状语,而加上连字符后,能且只能做名词的定语.
比如说：He is a hard-working man.他是一个勤奋的人.
This is a piece of up-to-date news.这是一条最新资讯.
至于不直接用14-year,这是因为英语中的固定用法,外国人的语言习惯是这样,我们不好更改.