Well, consent implies that they've thought about it and feel comfortable with it. Obviously teenagers (both girls and boys) should be taught that no one should make them feel like they have to have sex. Open and honest communication is part of consent, and any sexual encounter should have that. (Not saying you need to open yourself up completely to someone you're having sex with, but if you're not comfortable with telling them when to stop or what you're not okay with then no, you shouldn't be having sex with that person.)I think it is a naive view that sex is casual and can be had with many partners without emotional consequences. For both men and women. Nor are teenagers often emotionally mature enough to understand their own motivations for having sex. Especially at low maturity levels, the desire to fit in is probably the biggest reason kids do anything. Of course that extends to many situations beyond sex.
I don't know if you are advocating that point of view, but it seems like you are saying as long as the person is consenting it is cool whatever he or she chooses. I think that is naive. People consent all the time to things that are emotionally destructive. I don't advocate we do anything about the choices others make, but I certainly think it is terrible to council your kids that the most important thing in determining when you should have sex is consent. Obviously it is a requirement that both parties consent, but there are many other factors that should be weighed before taking that leap.
In any case, one of the factors that should be weighed should definitely not be: "You're respecting your body and yourself less if you have sex with more than x amount of partners or more than x amount of times."