I think that what is most important is taking into account your own child. Obviously, as a parent, you should impart your own experience to your kid, but remember that your example worked for YOU, and won't necessarily work for your child. If they are mature, responsible, fully aware of the consequences, and ready - then have at it. Obviously, you don't want the explicit details, but there doesn't seem any harm.
I'm not a parent, but I can totally understand the confusion of giving permission and being permissive - like, where do you draw the line? How young is TOO young? No matter how mature they are, I'd shut down a 12 year old wanting to have sex in about 3 seconds flat. Does that make me repressive and constrained to societal standards? Maybe, but I'm pulling out the 'so long as you live under my roof' clause. And if my kid runs away from a loving home simply to get some nookie, then obviously they weren't as mature as they think.
I remember at my sister's school there was a 14 year old girl dating a 27 year old boy. Apparently, she got permission form her parents. To this day, the thought of that still makes me queasy. Maybe her parents saw their kid could handle it, or maybe there was something wrong with them, but that NAMBLA shit wouldn't go down in my house. Again, MY house - you can do whatever you want, and at best, I'll try to see it from both sides. Doesn't mean I have to agree though.
You can only do your best as a parent. Remember that you can't expect either your child or yourself to be perfect - you're both going to screw up, maybe even epically at times. So long as you're there for each other at the end of the day, that's what counts. Be there for the advice, the mistakes, the scares and the joys and no matter how much warning and planning you do, expect the unexpected because life loves to mess with you. Just make sure to love your child through it all.