This 100%. I'm a millennial and I don't have these problems.. Why? Because my parents would constantly remind me to stand up straight, look someone in the eye when talking with them, give a firm handshake, show up early/on time, etc. I'm sure technology plays a role in some of the bad habits, but the whole being late thing is not a millennial problem.
I've had some millennial staff of mine send me a text to say that they're going to be late to a meeting, thinking that just informing someone of their tardiness makes the tardiness acceptable. When I try to explain to them that being late is being disrespectful to others, they don't get it. But when I equate it to Amazon promising them two day delivery, but not getting the package until 3 or 4 days later, they tell me "yea, that's f'ed up". unfortunately, trying to get some of these younger folks to think in someone else's shoes rather than only their own can be rather difficult.