@mathanxiety
So you're saying that because there are different problems for current teens than previous teens, current teens should not have sex?
As Moodypants said above, abstinence teaches nothing.
You're right. Easier access to porn has had an impact on what both boys AND girls are expected to do/look like/be like during sex. However as a responsible parent, I would try to teach my children that porn is NOT the same as sex, and to teach them to stand their ground when told otherwise. My advice would be the same to them regardless of their age, be it 16 or 36. Nobody should be copying porn as a foundation for lovemaking.
You help them to realise that their self worth does not depend on having a sexual relationship with someone.
How does telling them to avoid sex accomplish that goal?
I can tell my son that his self worth does not depend on playing football, and there are more important things in life than kicking a leather sphere around on grass. However that doesn't mean I would ever tell my son NOT to be GOOD at football, or that he shouldn't play at all. I would encourage him to be a rounded person by doing lots of different things that make him happy, including have sex with his girlfriend if they're both legal and both equally consenting.
It's people whose homes of origin left them vulnerable to be preyed on and these people would also be easy pickings for controlling teens. Embarking early on sexual relationships only reinforces the dysfunctional model for many girls.
From the sound of it, the OP's household is not resulting in a vulnerable young woman, rather a safe, loved and encouraged one with good self esteem.
You're right that damaged children can have their damage exacerbated by negative sexual relationships. However that is simply not the case here, and labelling all young people as damaged, or "at risk" or anything else doesn't help in the slightest. Would I recommend that a 16yr old drug addict sleep with her pusher for more drugs? No. Would I recommend that a 16yr old in a stable and loving romantic relationship sleep with her boyfriend? If she wants to, sure.
"Early" is also a relative term. You cannot put a number to it. How do you define "Early"? I know some 20yr olds who I wouldn't trust with a corkscrew, never mind sex. On the other hand I also know some 15yr olds who are extremely sensible and reliable, stay calm and make good decisions. An age of consent is important in a legal sense, but beyond that, you can't benchmark a human being. You can't say "Today you are not ready, but tomorrow you will be" when it comes to sex, because it's not an exam you pass or fail. It's entirely down to the individuals involved.
At the end of the day, helping your near-adult offspring make good decisions about priorities does not mean railroading them in the direction you want them to go. It's about them choosing what they want to do, and you guiding them, minimising damage, and talking about why/why not when it comes to making choices.