a seven-years child 有类似的用法吗

a seven-years child 有类似的用法吗 a seven-years child与a seven-year child哪个对?大耳朵英语网说前面的对?为什么? I___（am,was）a child seven years ago. I___（am,was）a child seven years ago.急 " a five-year plan. 一个五年计划"的YEAR不用加S,而 a seven-years child里的 I was a child two years ago.划 a child 和watch 有 类似用法的词 a few more years 有没有这样的用法?如果有 a few more 英语年龄的表达我知道She is seven years old 和She is a seven-year-old gi a fair knowledge and experience中的a 有类似这种用法吗? the child of three years old doesn't know there___(be)seven The first seven years 讲的是什么?