Earlier quoted context omitted.
I've seen grown adults behave this way with their phones. Totally zonked out and unaware of anything happening in the real world. Don't think it's an age thing.
I have a weird quirk that when talking to someone, if they start using their phone, I stop talking until they're done. It has made me painfully aware how true your comment is. Many times people don't even notice that I stopped talking (and why event try to talk to someone that isn't listening?)
At that point, might as well consider the next step of getting up and leaving.