Most moves in chess game ever

My opponent has a king and a knight.  I have a rook and a king.  Check mate is impossible unless one of us makes a mistake.  We are into 101 moves and I will not accept a draw because I lose points and he doesn't.  I don't really care.  It is just a game but then why not wait until his ranking goes up and then offer a draw.  I believe the rule is after 50 moves and no piece is captured an opponent who knows the rules can force a draw right?  If that is true what if he doesn't know the rules and does not force the draw.  How long can this game go on????