为什么不能说 a 8 years’old boy?

为什么不能说 a 8 years’old boy? 为什么要说the/a two-year-old boy 不能说two years old boy 为什么不能有a five years old boy 中间没有连字符 求详解 a ten years old boy和a ten-year-old boy哪个对?为什么? an 8 years old boy he is an 8 years old boy 为什么不对 Tommy is a boy.He is 8 years old. He is a sixteen-years-old boy a boy is fourteen years old 一个13岁的男孩能否翻译成a thirteen years old boy 如果不能,是否因为a thirteen ye 为什么不能说 how clever a boy he is he is a 6-year-old boy.可以说he is a 6 years old boy吗