Mine was not supervised cause immigrant parents that didn't know anything about computers really. So more or less entirely unsupervised.
By 16 I was regularly ignoring my parents to go to bed when I was up coding or gaming and doing dumb script kiddie stuff on IRC.
I had an adult introduce me to Astalavista (https://en.wikipedia.org/wiki/Astalavista.box.sk)
Thinking back to that I was very well aware of the fucked up part of the internet much more so than most adults around me. People did in fact meet up in person with strangers from the internet even back then.
I think it's more important to teach around age 10-14 about the dark side of the internet so that late teens can know how to stay safe. Rather than simply throwing them into the reality of it unprepared as "adults".
Also frankly I don't want to know the search history of a late teen. There's a degree of privacy everyone is entitled to.