I feel that negative emotion from periods on the last sentence (especially for messages that are only one sentence). So if you’re wondering what age range feels that way, you can consider 30 years old your upper bound :)

I disagree about receiving multiple messages in a row. To me, composing longer messages (especially with multiple paragraphs) feels much more formal; it’s like writing an email or a letter rather than having a conversation. I do sometimes write like that, but only on the rare occasion that I need to be particularly formal.