Family context also plays a role. My wife and I are “officially” Xennials, born a year apart in the late 70s. I have a brother seven years older than me, and she was the first born. I skew way more Gen X than she does, to the point where she doesn’t see any point in describing herself as anything other than a Millennial.

Named generations is a stupid concept in general. It's vaguely useful as a shorthand to talk about people's life experiences based on when they were born and how old they are now. But, it's mostly like astrology, saying that people born under a certain sign behave a certain way.