Annoyingly, the definitions are not actually well defined. But in
my head, I define them as such:
Born end of WW2 - mid 60s: Baby Boomers
Born mid 60s - mid 70s: Generation X
Born mid 70s - mid 90s: Generation Y
Born mid 90s+ : Millennials
Why do I group them as such?
Well Baby Boomers are very well defined, basically the oldest generation to live without any world war.
Generation X were far enough removed from the WWs to have the more rebellious nature that you can associate with hippies, disco types, punks and new wave. All your classic anti-conformists.
Generation Y were the ones to have more defined memories of before the digital revolution, growing up pre-internet, but being able to experience its rapid rise as teens/young adults. They also witnessed the significant acceleration of consumerism and marketing.
Millennials basically don't remember the pre-internet world, and are whiny little so-and-so's (for the most part)