As a former teen parent twice over you can imagine that we've had many sex discussions with our teens over the years. (Starting when they weren't teens lol.) I came from a home where sex was discussed in hushed tones so "little ears" couldn't hear, and where intimacy was treated as though it was dirty and embarrasing. All that made me think that sex was the greatest thing ever in a forbidden fruit kind of way. My mom said "You're too young to worry about sex." or "Don't do it until you are older and hopefully married."
So, armed with that glorious lack of info, raging hormones, and a well developed body I promptly went out and ran right into older men. I was 13. Jesus, what a recipe for disaster that was. The worst part was knowing that, even when I started to feel lost and overwhelmed, I couldn't turn to my Mom.
I got pregnant at 14 with Ds.
I know that was kinda OT, but it directly shaped how I have handled talking about sex with the kids. I've been very open, very willing to help them understand from a biological POV and the more mental/emotional/ personal perspective. No subject or question is off limits. (though I retain the right to some privacy about my own sex life in minute detail, of course. They don't want that info anyway though. )
I wanted them to know about birth control, body parts, diseases, and etc. I have also been very honest about the fact that I hope they will not take the same risks I did, and that I hope they think much more deeply about their sexual decisions than I did. I've been honest that I hope they are older than I was too. (I was 13) I am more comfortable with them having sexual partners at 17 than I would be at 15, but I don't think there is a golden age that I can say "Yep, that's it."
Bottom line? I don't care about them being married or not. I care about them being strong in themselves, educated, healthy, safe, and respected. What I want most is for them to be fully in control of their sexual decisions when the time comes, and to have far fewer regrets than I do. As far as when? Well, Ds is 16 and has never dated. Dd is going on 14 and isn't there yet either. By the time I was those ages I was a parent and working on #2. So far so good. If they start a sexual relationship and I have any concerns I'd share them just like I would about anything else. I see little reason to banish my sexually active teen to somewhere else to be intimate. It is their home as much as it is mine, and I have sex there so....?