When I was a tween or young teen, there weren't very many kids online or on the BBSes I used to use, so I talked to people of all ages all the time and probably annoyed them occasionally, but it was fine.
Eventually, my dad signed us up for something a bit more kid friendly/educational and we joined Prodigy.
Holy shit Prodigy was infested with paedophiles.
I think making something specifically for kids is a way bigger safeguarding concern than kids turning up to a thing not pitched at them, as long as there's no scope for DMs, but the people who wrote the rulesabout online interactions were Meta lobbyists, not people who actually have experience with being a kid in unsafe spaces.
Its not inherently bad to for a twelve year old to talk to an adult who is not related to them or paid to talk to them. For most of human history, its been normal. I had cross generational friendships at that age, one of which has lasted until the other person died of old age. (RIP Bob) These adults tended to be friends of my parents, adults I knew from volunteering or church, or sometimes neighbours. And one guy from a BBS.