You have a funny idea of when women become sexually active.
Two 13 year old virgins will not be spreading the viruses. The other dirty secret is the more people you have sex with the greater the risk which means the older people are the ones infected.
It takes some one to infect the young people first. In our modern world this could be the teacher.
Some one should take a look at the real disease carriers in the population. Gays first and the lesbians second then the black male and then yung 20 something white male population.
I keep hearing all these "I had sex once and I caught it" BS.
The truth is most people ( 90%) that will catch STD's will have sex many many time with many different people. We have a name for that.
Need I say it?