The words "Hey" and "Hello" are used differently, for different occasions. "Hey" is informal and can be used with friends you are close with or someone younger than you. "Hello" is more formal and is usually used with people older than you, such as seniors, at your workplace, when you are talking to a stranger, etc. When talking to someone for the first time and want to talk to them for the first time, you can say "Hey. My name is _______. Nice to meet you." (informal) or "Hello. My name is __________. Nice to meet you." (formal)

no, it's impolite to address seniors with "hey" because it's informal exclamation

Just stick with "hello". There's no problem with that. If you want to address a senior person, or someone you don't know, then you can also use, "Excuse me" to get their attention. Add "Sir" or "Ma'am" if you definitely want to be polite. If you use "hey", then you are being too familiar. I've written back to members who wrote their first email to me with "Hey Peachey" and asked them to learn some manners. If someone calls that to me back home, and they're not a friend, then they probably want a fight. As with any slang or casual speech, wait until the other speaker uses it first.

It is not polite to say 'hey' (name) to an elderly person. Hello is more respectful. Hi alsa ok.