I think that's a good question, Frida, and I think part of it is that people aren't honest with secondary school students about peer pressure. We got a lot of pressure from school, sex ed, PSHE etc to "wait till it feels right" and "don't be rushed", and even "Wait until Uni/you're older" - which makes sense apart from the fact that everyone in my school was at it from year 10,ish, (some outliers at year 9 and not until after school, but I think it averaged around years 10 or 11) and of course they were too young but at the same time they weren't really.
I suppose what I'm saying is that now I am a wizened in-my-30s-crone I've realised that the clumsy, awkward, thrilling/hurtful/boring sex I was having at any given point in my life was just... the right response to whatever situation I was in. I've had awesome sex in and out of relationships and pretty blah sex in and out of relationships too. I'd like to tell young people that 'being in a relationship' is no guarantee that your sexual partner won't be a totally horrible selfish nob, but knowing someone reasonably well is quite a good indicator in helping you work out whether or not you should have sex with them. Of course you can know someone well and still have sex with them on a casual basis - indeed, some of the best sex I've ever had has been 'casual but meaningful' - and it took me a good while to get rid of the virgin/whore dichotomy I was raised with, before I could start working out what I wanted, and then asserting it with partners.
Certainly, our young women and girls are raised to be pornified prudes, poor things, it's harder for them now than it was in the nineties. But how on earth can we discuss healthy sexuality with them, including peer pressure, enthusiastic consent, the whole shebang, while the rest of the world is so so so messed up about sex? I've seen "What you really really want" by Jaclyn Friedman, which seems to start from the right premise, which is that you should explore your body and feelings to work out what YOU life, before you begin a lifetime of pleasing others and being miserable.