I'm 22, 23 next month. The reason you're being labeled as a child is the way you type. The vibes people are getting from your messages/posts do convey a pre-teen person. Tone down the exclamation points and capitalize the beginning of sentences. Emotion Faces should probably be reserved for chats with friends or family as on the internet they are tied to younger people. Here's a re-written version of your post as an example:

"Whenever I post or talk to people on an online forum or something, they think that I'm a child or child-like. But I'm not, I am a 20 y/o. It's fine if they think that, but I think it's disrespectful."

Showering, I'll get to it eventually, and if someone reminds me i won't

I ditched Xitter ages ago yet this does not surprise me after everything that's happened

Just scrape off a layer under the toad, it's fine

I haven't seen Ahdok for a while, hope they're okay :(

Putting the Vatican below the Bible belt is going to be a disaster

There's literally no answer to this, infuriating

Oranges honestly don't have a braincell, though I think my Toffee (looks similar to the top of a cup of coffee) takes the cake

As an American, it confuses me as well