Green’s Dictionary of Slang

(US) an insignificant person, a whippersnapper.

1839		Congressional Globe Appendix 17 Jan. 105/3: There was not a Whig whiffet in the country but could ask [etc.] [DA].
1883		L.A. Lambert Notes on Ingersoll 200: We hold ourselves responsible to him, and to all the glib little whiffets of his shallow school [DA].
1920		Ade Hand-made Fables 121: A compact Huddle of He-Whiffets who sized him up with what seemed to be Gloomy Apprehension.