I was at secondary and sixth form in the 00s early to mid-late 00s. Sex was cool within parameters. Starting too early was weird somehow and to be too casual was unattractive and got you talked about. I went to a private all girls school for school years 7-11. It was always cool to know boys/ hang out with boys but I don't think as a year group on the whole, we really did very much more than kissing or occasionally a bit of fondling with any of these boys before roughly quite late on in year 10. So around 15 heading for 16.
The cooler girls had boyfriends and the loss of virginity started around then really, as a bit of a trickle that picked up in sixth form. Because we were so nearly legal, beyond a little curiosityw no one cared as long as you had a boyfriend- it was seen as normal. I remember someone a couple of years below me being viewed as REALLY slutty for having sex very young though. Anyone known for boyfriend pinching or being too casual about finding partners was judged. The faster starters were seen as a bit cool and could be a little patronising but it wasn't really much of a thing.
I think the school worried though as we had some very comprehensive sex ed in year 9 re stds and contraception. A friend who joined for sixth form mentioned the schools "notorious" teen pregnancy rate, heard from someone else in our year. This was news to me and I had been at the attached junior school too, and was well aware of loads of school lore! Certainly no one was ever known to pregnant and I think only 1 I know of ever "had to leave" because of it during my era. Only 1 in my year was ever rumoured to have had an abortion. No one really said anything but she was seen as a bit too keen behind her back. Anyone having a baby not long after leaving- that was their look out.
I went to a mixed, private sixth form with the same sort of vibe. A few people had slept with boyfriends in year 11 and they seemed the most grown up but no one cared in a negative way. It was a mixed sixth form attached to an all boys school so we got a lot of jokes etc but no one really judged sex with a boyfriend; we all did it during sixth form and no one cared as long as you were dating them and you weren't cheating. Cheating etc got you a rep - slutty for a girl, untrustworthy arsehole for a boy. I also recall boys with a supposed high body count not being seen as that attractive, either. They were seen as a bit obvious or sleazy. It was certainly a bigger deal to be gay than to be sexually active in a heterosexual relationship. Neither of the gay boys on my year came out til after school (after uni for one of them) and my openly bi friend was teased. She batted it off but it didn't go away until quite near the end of school. One guy is supposedly still in the closet.
We had some sex ed as girls from a nurse in lower sixth but it was less empowering or useful than I'd had before! I also know the MAP was available from the nurse (boarding school) as the girls once all got lectured about it being requested too frequently. It was supposedly aimed at the year above me - they were considered a golden year in terms of achievement etc. But they were legendary for boyfriend stealing, and lots of getting up to no good in various dark corners of the school.