这几种年龄的英语表述方法是否正确

题目

这几种年龄的英语表述方法是否正确
Most of them were only sixteen.
They were mostly sixteen-year-olds.sixteen-year-old是形容词吧?为什么加s
The boy the police arrested was only nine!
He was only a nine-year-old.形容词?
They are all 10 years old.
They're all ten-year-olds.跟第一例同问

答案

表述年龄应该是sixteen-year-old 或者sixteen years old
They were mostly sixteen-year-olds.sixteen-year-old在这里是名词,加了个S是因为是复数,泛指16岁的人,他们几乎都是16岁的人（孩子）.
同理 He was only a nine-year-old.nine-year-old 在这里也是名词,是单数不用加S.
第三句话同理参考第一句.