I think it’s meaningless, and part of a media (and societal) obsession with labeling. Let’s take the Boomers, for example. Someone born in 1946 came of age during the Vietnam War era and the turmoil and social changes of the 1960’s, while someone born in the early 60’s (tail end of the Boomers) came of age when Reagan was president.
If you follow the classifications in the original question above, someone born in 1925 would have been old enough to have been in World War II (not to mention having been aware of the economic turmoil of the 1930’s), while a junior member of that same broad classification entered adulthood at the end of the 50’s—a completely different world, really.
It’s fun to play with, but I think it’s oversimplified and doesn’t really reflect the realities of our shared existence (except maybe for the folks at Time-Life).