Love is caring about the freedom of the other. A man who really loves a woman will never force her. That is why rape is so awful. Many of the great artists have loved to paint the female body. There is a big difference between the artistic appreciation of beauty, and treating women as sex objects.
Magazines are pornographic when women are pictured as sex objects to be abused.
In Playboy magazine some of the women are photographed very tastefully. Let your son see that you are not embarrassed by these questions, and are prepared to express the distinctions that are important to you. He may not say anything immediately, but slowly he will gain confidence that you are not horrified by his male sexual feelings. If you do find your son reading Playboy magazine, rather than hit the roof and go into a tantrum, you could surprise him. Let me see which of these girls I would l like you to marry.