Personally I think that 2 years is pushing it. In school I always stuck to a 1 year rule. This being said, a few of my friends have dates girls either 2 years above or bellow and they seemed perfectly happy, although the relationships did not last past 6 months.
To be honest, it should not matter what we say, or what anyone else has to say. If you feel strongly about it, which you clearly do as you said you are dating her, not are thinking about it etc, then stick with it.