This is a 2-in-1 question, I suppose. I type the way I do. I’ve always typed this way, but I’ve noticed when interacting with people (not on here) that people always think I’m far older than 19. They think I’m in my forties or fifties.
Also, I tend to type using full stops, which people may think are rude. When I’m typing a full sentence, though, I end it with a period. If I say, “He’s being an asshole,” (with a period), I mean that as a fact, not out of anger. It just happens to be ended with a period since it’s a sentence.
I have found that I always use proper punctuation in informal communication except for a period at the end of a message. If the last sentence is a question or exclamation, I’ll use a question mark or exclamation point. But if it technically requires a period: usually nothing.
Then again, I am in my forties or fifties