that means you know less people! simple!

just think about it -

８０年代留学生 who come to study in USA at 1987, 27 years old, at least have kids around those years, then kids born in 1987 should be 23 years old now; kids born earlier than that are even older.

So look around and check 'chinese faced boy/girls' whose parents are from mainland china in USA, you will find a lot of them in 20-30 age frame.