To me, sentences ending in a period feel immutable, and without nuance, but sentences without a period feel incomplete, or up to change. Without periods it is almost a way to say, “this is what I think right now, but I might reconsider.” So, it’s not that periods are rude per-se, but it may appear that you’ve made up your mind and are closed off to interpretation. Sometimes I intentionally remove periods or turn it into an ellipsis for exactly that reason. It’s just way too easy to misinterpret people’s intentions through text for me not to type in a way I think reduces misinterpretation.
As for being associated with older people… anecdotally speaking, my co workers sound like they were taught that there is an immutable, proper way in the world, and so they express themself in that proper way. Nothing wrong with that really! Once I get a feel for their personality, I find it kind of endearing :)
this might not be what you meant, but the word “tar” made me think of tar.gz. Don’t most sites compress the HTTP response body with gzip? What’s to stop you from sending a zip bomb over the network?