When I was a lad his age中的his age是作为何成分

When I was a lad his age I would laugh at the strangest things.

我是他那样的小毛孩时，莫明其妙地就会发笑。

请教这句话中的【his age】是作为何成分呢？

his age是名词短语作后置定语。其实，a lad his age是a lad of his age的省略形式，of sbs age“像某人那样大；与某人同龄”是介词短语，且of常可省略，省略后应将它看作是名词短语，常用作表语或定语。如：

She is my age.她与我同龄。《简明英汉词典》（表语）

They are the same age.他们两人同年。《现代英语惯使用方法词典》（表语）

a boy your age像你那样大的男生《现代英语惯使用方法词典》（定语）

We have a sonyour age.大家有个儿子和你同岁。《牛津高阶英汉双解词典》（定语）