He is very green
贴切的翻译应该是： 他还很嫩
这句英文是明显的口语体,现在的口语一般有两种方向：一种是粗俗化,一种是委婉语.其中相差很多.后者一般用于正式场合,对应表达为：It seems that he is somewhat unfamiliar with that.