From pwn + -age.
pwnage (usually uncountable, plural pwnages)
- (Internet slang, leetspeak) Ownage; the act of pwning.
2001 September 22, Kix, “Re: lo all”, in uk.games.computer.counterstrike[1] (Usenet), retrieved 2016-09-23, message-ID <[email protected]>:"OMDFDG LOOK AT THIS PWNAGE SCORE!!"