Why do some 13-15 year olds want sex?

[Maya]

I'm 13 years old and I find myself constantly wanting it.
And before someone says it's because of pressure from media or peers, it actually isn't. I haven't felt any pressure into having it. This came naturally and slowly, but I'm still confused as to why I feel it at 13.
I have a boyfriend, and I know people will say "You can't have a serious boyfriend at the age of 13!" Well, it's as serious as it can be when you're 13. On a daily basis, we often share our feelings and thoughts with each other, and we both feel that same wanting. Again, my boyfriend and I aren't the type to give in to pressure or media hype. Our wanting came naturally, and we found ourselves craving sex from each other. I think about it often, and he does too. (BTW, before anyone calls me a slut, I haven't had sex or done anything sexual yet)
Despite my urges, I made a promise to myself to wait until marriage, and to wait until I have my education and my career set. But why do I crave this at 13 years old?

[Guinea Pig Mama]

You have that desire because it is human (animal, actually) nature to desire sex at that age. The body is preparing itself to reproduce and in turn you have an innate desire to do so. It is not due to "pressure" or "media". It is the development of the brain and it is a normal part of life. Everyone craves it at your age, its just that some kids are more distracted with social activities or sports so that takes their mind off it but deep down I believe everyone has those kind of thoughts when they are 13. I certainly did.

[Jamieson]

Because they don't know how to control their hormones and keep it in their pants.

[Mad about 69]

Hormones and the need to reproduce once puberty hits, its in our DNA but the law looks at it another way. One thing to remember is that not all teens are emotionally ready to handle all that goes with sex which can cause psychological problems so should only do it when everything feels just right and not be pushed into sex for what ever reason.