See, the term "Explicit" seems to be thrown around a lot here. The rating TEEN specifically has the point 'Suggestive Themes" which would include minor acts that may have a a sexual undertone to it. Two characters slowly making out. A hand slowly rising up someone's thigh. It may even get a bit more heated with someone taking their clothes off or nudity.
However, as long as the details are limited, this wouldn't be explicit. It would be well...suggestive.
Explicit is when there's a specific detail and expression of, in this case, sexual activity. Genitalia is shown, specifically for the sake of sexual eroticism. Intercourse is shown distinctively and not merely through suggestion.
Let's also not forget that "TEEN" encompasses a wider range of ages than just 13. It's basically 12-19 and some would even argue could go as high as 20-21. It's basically expected that by this age, people should have some kind of understanding of sexual behavior.
Erotica doesn't corrupt or hurt teens. You know what does? Improper and lack of education on sexual matters. This is why abstinence is the biggest joke. Teens are going to have sex whether you like it or not, so its best to both properly educate them and give them the tools as well.
This is why some schools offer condoms to their students during sexual education. They'll even show (indirectly) how to use them and you'll see how these schools have lower levels of teen pregnancies under their name than a school that tries to advocate abstinence only.
Society, especially in the west, has tried to demonize an act and feeling that is both natural and healthy. Imagine how many times someone, probably even you, heard about how terrible masturbation was. That if you touched yourself, horrible things would happen and you'd become a leper. This ideology permeates the minds of so many people.
They have these urges that they're told is bad but have no way to express it. They bottle it up, building up on negative feelings until it finally breaks out...and not in a good way. I believe it was Woody Allen who once said. If you're not comfortable with touching yourself, why would you ever want to have sex in the first place and have someone else touching you?
Quite frankly, people need to start looking beyond the foggy glass and see the real world in front of them.