请问X-year-old和X years old 的区分和具体用法?还有 X－year－olds

请问X-year-old和X years old 的区分和具体用法?还有 X－year－olds 请问twenty-year-old和twenty years old的区别什么时候该用twenty-year-old,什么时候该用twenty years old years old 和year-old的区别和用法 year old,year-old,years old,years-old的区别 fourteen year old和fourteen years old和fourteen-year-old和fourteen-years-old的区别 ten years old 和ten-year-old的区别 three-year-old 和 three years old 有什么区别 three -year-old 和 three years old有什么区别? 11-year-old和11 years old有什么区别 seven years old和even-year-old的区别 12 -year-old 和12 years old的区别 six years old 和 six- year- old 和 six- year- olds的区别如题 16-year-old和16-year-olds和16 years old有什么区别? 请问是six-year-old还是six years old还是six-years-old?(这个空签名有个a ) 16-years-old和16-year-olds的区别 year olds还是years old? eight years old与eight- year-old year-old与years old的区别