Re: Millenial/Gen X
I think part of the handwaving definitions include internet in the house as you were growing up. That seems to be a defining part of the shared culture. (All your base etc) That will vary from household to household.
If you are old enough to think the internet is newfangled, you're probably not a millenial.
If you are young enough to think smartphones and tablets *aren't* newfangled, then you're too young to be a millenial. <- my personal addition
(age range as of 2018 covers approximately 25-37)