OP, as a parent whose kids grew up online, I'll give the same advice I gave to my own kids:
Lurk all you want. Chat politely sometimes. Don't tell anyone how old you are.
(We used to know that "A/S/L?" meaning "age, sex, location?" in a chatroom was a sure sign of a creep. I hate that it's become common to put that info in your profile.)
Do not provide verification for your age. (Get comfortable asking, "What are you, a cop?") Don't give out your real name, the city you live in, where you to go school, or ideally, what region or state you live in. NOBODY ONLINE NEEDS TO KNOW THESE THINGS.
(Yeah, you'll lose out on some merch that way, unless you have a local adult who's willing to be an address for you.)
Do not meet with anyone. Do not give out your phone number. Ideally, don't give out your email, or make a separate one for your "I'm an adult, really" account.
Talk to YOUR parents, or another trusted relative or adult mentor, about your worries. Please. It's important to have an adult you can trust, who can help you spot the difference between "those are just grownups talking about grownup stuff" and "those are f'n predators; stay away from them."
Safety doesn't come from sticking with your own age group. There are predator teens, AND there are predator adults who pretend to be teens. And teens can't usually recognize them.
Safety comes from seeing a broad range of communications, including about sensitive topics, so that you know what's normal and what seems creepy. Safety comes from not giving people contact info they don't need for online activities. Safety comes from recognizing when a conversation makes you uncomfortable, and quitting it - and blocking the other person or people involved, if you want. Safety comes from seeing people argue badly and the apologize awkwardly, so you realize that anger isn't a dangerous emotion on its own. Safety comes from learning where your boundaries are, which means going places where you might reach them.
SAFETY DOES NOT COME FROM IGNORANCE. It does not come from isolation. If you're mature enough to be on Tumblr asking anonymous questions, you know enough to put yourself at risk. From here on out, safety comes from knowledge and practice.
So practice in ways that can't get to you physically: in places where nobody knows your real name or where you live or how to contact you, so that if you drop out of a Discord you have effectively vanished.
(I am so damn sick of ageism in fandom. All the "separate areas for minors and adults!!!" thing does, is leave minors vulnerable to predators and guarantees they'll keep that vulnerability into their mid-20s.)
Small caveat: Laws about what's legal to share with minors vary by country and state. Go learn yours. Please avoid tricking adults into committing felonies by letting you see art that's illegal for you to see.
But as far as 90% of fandom discussions? Age is irrelevant, and I wish more communities would acknowledge that consciously instead of setting up a system where the rule is, "minors can be here if they lie."