As Frank has intimated, these generation-names are the tools of people involved in advertising/marketing. They invented them (with the exception of "The Greatest Generation" which was invented by Tom Brokaw). Each "generational cohort" is characterized by unique buying habits, and these are critical bits of information for those whose business is selling - so to standardize their discussions within their industry, they've adopted these names. Their designations have been borrowed by students of sociology for shorthand in their theses and dissertations. From there, they've leaked into the mass media and on into public discussion. The terms are really meaningless on the individual level. They were never intended to be a descriptor of any individual.
As for which cohort your buying habits will most resemble - that probably will have to do with those of your parents and friends. You could think of it this way, if you wish to remain hung-up on these terms: If your parents were Boomers, then your buying habits might end up resembling those of Gen X. If your parents were Gen X, then your habits might be more like those of Millennials. Of course, that depends a lot on you, personally, since you might not fit either cohort's profile at all.
(btw: Many people were born in 1997 to Boomer parents, but no one was born in 1997 to Millennial parents, so Gen Z is not a possibility.)