An exceptionally large part of dignity is restraining your own freedoms.
No, it isn't.
Dignity includes your right to be treated like an autonomous individual. Not as a tool to facilitate someone else's pleasure, whether that be their sexual gratification or their moral comfort. Dignity expresses something that is actually fundamental to "Western society", even if said society has often failed to live up to it, and that is the idea that a human being owns themselves.
Fewer teens than ever are having sex.
While those are cherry-picked numbers within the fairly wide variety of statistics on the subject, it's pretty undeniable that this is true. However, it's also pretty universally agreed that the primary reason for this has been the rise in the quality and availability of sex education and a more open societal attitudes towards the discussion of sex and intimacy, not some great resurgence of dubiously "Christian" morality.
When you survey people who will have been teenagers a couple of decades ago. A significant proportion of them (generally around 1 in 5, mostly girls) will tell you that at the time they lost their virginity they didn't feel ready to do so, but were experiencing pressure from a partner or from peers. It turns out, when you teach children that they have no control or agency within their own lives and that their wishes and enjoyment do not matter and that they aren't supposed to think or ask about sex, they will take that assumption into their sex lives.
Sexual culture of the late 90s and early 2000s was incredibly toxic, and a big part of that was the complete sidelining of any idea of pleasure, especially pleasure for women. Shutting down any kind of frank discussion around sex doesn't make people stop thinking about it, it just makes the discourse around it dirtier and more brutal.
The inevitability you speak of is genuinely rare, and as best as I can tell, the only people who think horny teens are all over each other are recluses envious of the sexual society in their imagination.
Depending on how heteronormatively you measure it, I lost my virginity some time between the ages of 14 and 16. I have never regretted or felt bad about it. The person I lost my virginity to remains one of my closest friends.
People mature at different rates. For me, it was like a switch flipped one day and I went from having little crushes on people I thought were really nice to actually being physically aware of what I wanted. Around that time, I briefly dated someone in the year below me (so around 13) who was very much in the same headspace and clearly expected me to deliver, although nothing happened as I wasn't really comfortable with the age difference.
But here's the thing. When I lost my virginity most kids in my year, boys especially, weren't even really thinking about it. They were curious about sex and they liked dirty jokes because it was taboo and thus funny, but they weren't really sure what they wanted. But there was very definitely a minority of us who were either sexually active or who felt ready to be, and it was not really a secret to anyone. Kids who want to have sex will either find each other, or they will attempt to introduce sex to the kids who haven't really thought about it yet, and in the grand scheme of things the former is preferable.