I guess I missed the memo where we all agreed that teens should abstain from sex to make William Saletan happy. Or something.
But, no, I don't think the ideal amount of teen sex is zero. I think the ideal amount of teen sex is whatever amount of safe and consensual sex between people who have a reasonable understanding of what they're getting up to want to have. We freak out about teen sex because we freak out about sex generally, and more specifically female sex drive, and we screw up a new generation of people by convincing them that "waiting" is the "right" thing to do and sex is somehow wrong, especially because, but not limited to, the fact that we set up women to be the "check" on male sex drive.