Teenage Pregnancy: My Selfish Gene Theory

I have been reading "The Selfish Gene" by Richard Dawkins recently. Considering my knowledge of genetics is rudimentary at best and my understanding of evolution is not much better I felt that it would be worth reading into these fields so I could hold my own in a conversation. I am about two thirds of the way through the book and it is enlightening. I shouldn't really call it a book I suppose, it is more like one huge argument by someone who is extremely arrogant and self important. That being said the argument is compelling and in the field of Ethnology, Dawkins is quite important. I am not sure if I want to read his newer books about religion because having seen his rants in movies like Religulous or on The Colbert Report, I cannot distinguish his view from that of Evangelicals. He is essentially an evangelical atheist. I don't care for those people on the fringe who have no interest in listening.
The interesting thing about The Selfish Gene is it doesn't just explain how using the gene as the evolutionary unit that evolution would take place but gives you the tools to think in a genetic-based-evolution way. By the third chapter when he frames a new experiment you cannot help but stop reading for a few minutes and think about the puzzle and try to use the tools gained thus far to work out a solution. It really teaches a new way to think. It isn't long before you start thinking about other things with regard to the selfish gene. So here is my completely uneducated evolutionary stable idea:

If we assume that men and women are dirt sluts until marriage and after marriage are wholly monogamous, then it stands to reason that evolution would favour genes that promote premarital pregnancy since after marriage if one partner is not virile/fertile than neither person can procreate. Whereas those who seek to impregnate/be impregnated before this switch in sexual behaviour from filthy sluttery to monogamy will be more likely to produce offspring.