People should have sex and experience sexual activity with someone they care about when they feel ready. That for me is the bottom line. Age (to a degree) is irrelevant, because people develop at different times.
I do believe of course for the first time the two people should be close in age, simply because sexual predators and those taking advantage of younger individuals and all that, that is not good. But my point is, if two people who both are 14-16 feel ready, genuinely like each other, and somehow fumble their way into it and have sex one night, this is NATURAL. Can we really deny that what they did was anything less than natural?
And this is out of our hands in a sense. If they're gonna do it, they're gonna do it. Why run around trying to control them? More importantly, if its going to happen what is our responsibility as a society?
1) Educate them so they do it safely. Educate means give them information about the pros and cons so it will have been their decision, and it also entails giving them the means to do it safely. (birth control, etc)
2) Not apply weird social ills like religion, guilt, pressure, badges, rings, etc., to the equation, so as not to warp their mentality and make them feel as though they've done something dirty or wrong.
I also firmly believe that when repressive adults (adults who missed out on it themselves, are conservative, sexually repressed themselves, bitter, jealous, overly religious, etc) apply their thinking to young people and warp their minds about the role of sex (it's evil, you'll go to hell, masturbation is evil, condoms are evil, you should wait, you're not ready,) it in turn warps young peoples minds and this is in a sense a mild form of abuse. It prevents normal mature sexual development (sexual development is not ALL physical, the mental aspect is equally critical)
Teens suffering from extreme guilt, pressure, conflicting views, lack of education, fear, etc., this kind of influence leads to sexual misfunction, sexual deviance, poor development of relationship skills, many problems. You're stunting their growth instead of accepting it and guiding it in the most helpful way. It's akin in my mind to things like female circumcision, foot binding, etc.
Just my 2 cents.