I understand the OP to say that no statements relating to gender differences are universally true. It is a challenge to demonstrate that the assertion is false since it takes only one counter example to prove lack of universality.
The absence of a universal case is, however, something quite different from the proposition that generalizations are always false. In our flight from universal statements, let's not abandon conversation necessitating use of generalities. When one says, for example, that women earn less than men, don't we understand that we are saying that IN GENERAL (or as an average or some other statistic) women earn less than men? Isn't the perjorative "generalized stereotyping" just a stereotype that we have concluded is objectively inaccurate?