I'm not sure if it's an age thing, but if you're asking me for something in an email, I really don't care if you address me by first name.
However, please use appropriate professional email etiquette.
So if you sent me an email, start with "Miss Violet" or even my first name.
But do not start your email off with "Hey."
I get emails from students all the time asking for different things and they look like this:
"Hey, I was just wondering if you could write/send/do ___________. Thanks, Student."
I'm not old by any means, but I'm also not one of your friends. So "Hey" is not a good way to address me when you need me to do something for you. I wouldn't address a student with "hey."
And it wouldn't hurt for you to say please, either. Notice that nowhere in my above student email does this person say please.
"Remember that apathy has no place in our Sorority." - Kelly Jo Karnes, Pi