I'd think it's probably not a majority, but I do wonder what percentage it actually is. I do have distinct memories of being like 12 and trying to find porn of people my own age instead of "gross old people" and being confused why I couldn't find anything. Kids are stupid lol, that's why laws protecting them need to exist.
Also good god when I become a parent I am going to do proper network monitoring; in hindsight I should not have been left unattended on the internet at 12.