I have never been a wife of a porn viewer but I just want to add a touch of reality - there is nothing deeply wrong in the attraction of a 40 year old male to an adult 20 year old female, and given the current practices on the age of acquiring your first born, no, you would not be a father to 20 year old women.

I think there should be some conversations between the two of you to get her in touch with reality as well - she seems to be very far from it.

Nor do you have an obligation to feel paternal to anonymous women who were hopefully paid to perform in porn. If you want to feel paternal to strangers (beyond what you do by fathering your own children), try fostering a child. It would make MUCH more practical sense then believing that your not watching the screen images of 20 year old women would contribute to the happiness of the humankind.

Good luck!