What is criterion for a game being considered retro/classic/old(school)?

[richardhutnik]

The Ghost of RubangB said:

Retro is before 3-D. I can't consider Mario 64 retro, because games like it are still being made.

Oldschool is either old games or new games in the oldschool style, like the new Punch-Out!! or Viewtiful Joe.

Do you mean "before the use of shaded polygons"?  I would consider Zaxxon and Battlezone to fit into retro/classic/old(school).