Fandom as a whole is not “minor-friendly”
Nor should it be.
If you want to live in a “Children of the Corn”-style bubble of innocence and purity, well, to me, that’s a startling approach to adolescence, but every generation’s got to find its own way to reject the one before, so: do as you will. But you can’t bring the bubble to the party, kids. Fandom, established media-style fandom, was by and for adults before some of your parents were born now. You don’t get to show up and demand that everyone suddenly change their ways because you’re a minor and you want to enjoy the benefits of adult creative activity without the bits that make you uncomfortable. If you think you’re old enough to be roaming the Internet unsupervised, then you also think you’re old enough to be working out your limits by experience, like everybody else, like I did when I was underage and lying about it online. If you’re not old enough to be roaming the Internet unsupervised and you’re doing it anyway, then that’s on your parents, not on fandom.
If you were only reading fic rated G on AO3, if you had the various safe modes on other media enabled, you would be encountering very little disturbing material, anyway (at least in the crude way people tend to define “disturbing” these days; some of the most frankly horrifying art I have ever engaged with would have been rated PG at most under present systems, but none of that kind of work ever seems to draw your protests). In the end, what you really want is to be able to seek out the edges of your little world, but be able to blame other people when you don’t like what you find. Sorry. Adolescence is when you get to stop expecting others to pad your world for you and start experiencing the actual consequences of the risks you take, including feeling appalled and revolted at what other people think and feel.
Now, ironically, fandom’s actually a fairly good place for such risk-taking, as, for the most part, you control whether you engage and you can choose the level of your engagement. You can leave a site, blacklist something, stop reading an author, walk away from your computer. Are there actual people (as opposed to works of art, which cannot engage with you unless you engage with them) who will take advantage of you in fandom? Of course there are. Unfortunately, such people are everywhere. They will be there however “innocent” and “wholesome” the environment appears to be, superficially. That’s evil for you. There are abusers in elementary school. There are abusers in scout troops. There are abusers in houses of worship. Shutting down adult creative activity because you happen to be in the vicinity isn’t going to change any of that. It may help you avoid some of those icky feelings that you get when you think about sex (and you live in a rape culture, those feelings are actually understandable, even if your coping techniques are terrible), but no one, except maybe your parents, has a moral imperative to help you avoid those.
In the end, you’re not my kid and you’re not my intended audience. I’m under no obligation to imagine only healthy, wholesome relationships between people for your benefit. Until you’re old enough to understand that the world is not exclusively made up of people whose responsibility it is to protect you from your own decisions, yes, you’re too young for established media fandom. Fandom shouldn’t be “friendly” to you.