I am close to 40. In my year at school, even allowing for those who claimed to be sexually active but weren't, I'd say about 30% of girls were having sex by the age of 13. Well over half by the age of 15. I thought the average age for a girl to lose her virginity these days was about 13.
The trouble with sex ed is that in a perfect world it would be unnecessary, because no child would want to do it before the age of consent and all parents would have lengthy, informed discussions with their children about sexual health and safety and emotional wellbeing. But it's not a perfect world, is it. And we would be failing the very many children who don't get this support from any other source if we withdraw it from schools.
My DC knew the biology of sex and how babies were created by the age of 5, including the various body part names and the egg and sperm bit. Obviously their understanding was a little bit different to your average year 7's, but IMO if they're old enough to ask, they're old enough to be given an age-appropriate explanation.
Exposing children to porn (the average age of that is also 11
) and the constant sexualisation of our society are far more worrying to me than sex education in schools, though sex ed could be used to far greater effect to counteract some of the highly damaging messages directed at our youth through these means IMO.
Before industrialisation, most children of a surprisingly young age (bar the aristocracy) would have been completely au fait with the mechanics of sex. It's not going to traumatise them. We need to concentrate far more on contraception, STI prevention and why it's perfectly ok to say no either to an act that makes you uncomfortable or to having sex at all.