I was 23 and well aware that I was an outlier at that point!
I was a late bloomer in that I went through puberty quite late in for some reason, was a few weeks away from my 16th birthday before I started my periods and starting to worry there was something terribly wrong with me etc. So I looked like a little girl until about 17, doubly hard to deal with as I was one of the youngest in the year anyway. And was also very academic with quite a sheltered home life in a very Christian family. So not exactly part of the cool crowd at school although I envied them! My friends were similarly geeky etc (albeit mostly not religious) but most of them lost their virginity around 17/18 when they started dating (one of them at 15 which we all found quite shocking at the time although we were also aware many girls in our year at a mixed state school in N Ireland in the mid to late 1990s were having sex around about 15 (or as young as 13/14 if you were in the cool crowd) - just didn’t expect one of our own crowd to be quite so “trendy”! I would say looking back that this friend was actually the victim of mild child neglect with alcoholic parents, although I hadn’t totally framed it as such in my head at the time, and I suspect that played a role in her having sex earlier than the rest of our deeply uncool friendship group. And I’d say actually that a lot of the cool crowd also had rather unhappy chaotic unstable home lives etc. Many of the girls who had sex particularly young (like under 15) it was with much older boyfriends. I envied those girls at the time and thought they seemed so mature etc, but honestly I look back on it now and think what fully grown man in their 20s (and in some cases 30s) wants to go out with a 13/14 year old schoolgirl?!...
I didn’t have a boyfriend til I was 18 after I left school. And had originally intended to wait until marriage to have sex for religious reasons, hence no sex with that boyfriend (I felt a strong urge to make that a sexual relationship, and if it was not for my religious beliefs I likely would have, but managed to resist and it was easier to keep it non-sexual as he was a virgin too - he was from another culture, I met him on my gap year in SE Asia and he was a local). However I didn’t manage it in the end and decided age 23 to have sex with my uni boyfriend of 2 years.
He had split up with me the preceding summer, I think partly due to sexual frustration although he didn’t spell that out to me at the time. He had respected my beliefs about waiting for marriage but didn’t share them as he was not Christian, so didn’t pressure me to have sex, but he had previously been sexually active and I think he found it understandably difficult to be in a relationship with me without sex being part of it. Anyway, when we saw each other again on the first day back at uni we got back together immediately as we’d missed each other so much, and I told him I’d changed my mind.
Looking back I still feel slightly conflicted about that decision, as essentially I was then in a situation where although he wasn’t intentionally putting pressure on me to have sex, I did feel like I would “lose” him if I didn’t. And slightly wish I’d had the courage of my convictions as I am still a Christian, and continue to feel some guilt over being sexually active before marriage despite my beliefs.
At the same time, I have I think always had a naturally high sex drive and had been finding it increasingly frustrating and difficult myself to not be having sex with him, as it felt completely natural to move to that from kissing etc. And I have to say that the sex was completely amazing, fun and tender with him, including my first time. Also my later husband (a different person - ultimately split up with the uni boyfriend as we just didn’t want the same things in life eg he didn’t eventually want marriage and kids, I did etc) unfortunately turned out to be a compete bastard who cheated on me and subjected me to domestic abuse, so I have to say I’m still now quite glad in a way that I didn’t “save myself for my husband”. There is also part of me that thinks God created us to be sexual beings and that in Biblical times, waiting for marriage certainly didn’t mean into your 30s potentially. Against that, I do also sometimes think that perhaps relationships and my life generally might all have turned out differently (and better) had I managed to follow my faith better and perhaps sought out more Christian friends to help me do that, and perhaps I let myself down in terms of following my own script and not God’s, hence the serious problems I have faced with domestic abuse etc.
Anyway, overall I think I don’t regret the decision. It was a very positive first sexual experience for me, and I felt very relaxed and secure within the context of a loving relationship with someone I knew very well, we were like best friends as well as sexual partners and although it didn’t work out ultimately, while it lasted it was I think a mutually good and healthy relationship, and not just sexually. And I felt in control and mature enough to handle everything that comes along with sex, including not just the emotions but the practical stuff like getting STD tests before being sexually active with each other and having to go to ask the pharmacist for the morning after pill when the condom split one time even though it’s embarrassing etc.
To answer your question about how young is too young, I do think teens can mature at wildly different rates but I suspect 13 or even 14 is way too young for the huge majority (although I believe I have met some girls that age who can definitely handle it), and definitely 12 would leave me feeling really quite shocked and worrying about sexual abuse. I reckon the huge majority of girls are nowhere near ready til about 17/18. I suspect that religious issues aside, I’d have been ready at 18 but I also think I did benefit from having those few extra years to feel super comfortable and confident about having sex to the point of being able to not only deal with emotions and logistics but have really satisfying sex through honest conversations with my boyfriend about what was or was not working for me, what I wanted to try and what i really didn’t etc.