N-COUNT 自以为是的人;妄自尊大的人 If you refer to a young person as a whippersnapper, you disapprove of them because you think that they are behaving more confidently than they should. 自以为是的人;妄自尊大的人 [informal, old-fashioned, disapproval]
...this bunch of irresponsible young whippersnappers.