...And an easy one to make.
Jenova is perhaps one of the least involved FF villains ever, if you go by her level of direct involvement in events during the game.

In answer to masamune1287's original topic, though... the issue of Vincent's age and Sephiroth's age is one that just keeps coming back. The fact that Mr Valentine (SPOILER)spent decades in suspended animation is never directly addressed in the game, at least not in relation to the way it affects his age.