It’s not that arbitrary. Gen-X are the first generation of boomer children. Millennials are the second generation of boomer children who grew up with the internet. These are real events.
People find it easy to fit boomers into a tidy box. Ask the boomers born on the cusp of boomer and gen-x. It’s arbitrary bullshit too. It’s not like baby boomers all came from the boomer factory and then one day they decided, ‘that’s it the boomer factory’s closed’.
They fell in love with their own reflection. All they can hear is their own words ‘Freedom!’ echoing in their ears. It’s a modern day tale of Narcissus.