I have run accross this topic in other forums and generally the comments run in the same form. The "Age of Consent" topic is one that can push many buttons and start mini-wars.
That being said, IMHO, the biggest problem is how society views a juveniles actions and the repercussions visited upon him or her if the knowledge of sexual activity becomes known. I mentor sixth, seventh, and eighth grade (middle school) students and one of the questions that always seems to come up is when can I have sex. Of course, physically they are capable now. My answer to them usually involves a mini lecture on STDs and pregnancy prevention, then I try to provoke their own thoughts on the question of readiness. One item I bring up is: "Are you ready for your parents to know you are sexually active?" That usually brings them up short with 'no telling' stutters and such but I counter with at least two people will know the secret, and a secret is not a secret if more than one is in on it.
I was asked an interesting question the other day. A seventh grader was complaining all his friends were riding him because he asked a 12 YO girl (sixth grade) to a school dance. They accused him of robbing the cradle. As it turns out he had barely turned 13 himself, just missing the cut off for waiting a year to start school. This indicates to me that the societal stigmas of age vs sex are apparent even at the middle school level.
Just my two cents.