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.
It’s simply linguistic evolution, and I find it interesting how the internet has shaped language. Writing on the internet tends to be very short and conversation-like, so if you want to get a point across there’s no need for a full stop. This meant, that when people put full stops at the end of messages on the internet, it started being seen as more formal and serious, which became a tone marker