I have a 12y in year 8 and a few of her friends are now 13y and the rest will turn 13 this year.
Dd and her friends are nowhere near having sex. They aren't really even having boyfriends and certainly none in dd's social group have even had their first proper kids yes, let alone anything more.
Even growing up I don't remember anyone at this age having sex. A year or two later I knew of two people - with each other. Rest it wasn't til sixth form.
When I taught secondary a small minority of young ones talked about having sex. However, it wasn't common and the vast majority were nowhere bear that stage at 13.
It just isn't the norm in my experience. Thankfully IMO.
I've taught a lot of 13 year olds over the years and have never yet met one of them who was really mature enough to deal with a sexual relationship, especially if it went wrong.
I do think it is something we should be discouraging and be pointing out the legal implications as well as the emotional ones.