this is a eight-year-old boy eight-year-old 是形容词八岁大的 一中构词法 注意year是单数
This is an eight-year-old boy.
或This is a boy who is eight years old.
this is a boy who is eight years old.
this is a eight-year-old boy.
this is a boy at the age of eight.
This is a eight years old boy.
This is an eight-year-old young boy.