Source : Webster's Revised Unabridged Dictionary (1913)

Whippersnapper \Whip"per*snap`per\, n.
   A diminutive, insignificant, or presumptuous person.
   [Colloq.] ``Little whippersnappers like you.'' --T. Hughes.

Source : WordNet®

whippersnapper
     n : someone who is unimportant but cheeky and presumptuous [syn:
          {jackanapes}, {lightweight}]