Yeah, I'm a late Gen-X'er... born in the 70's but too young to remember any of it.

Some of the categories and age ranges were influenced by the authors Strauss and Howe who wrote "Generations" and "The Fourth Turning". I've read the latter book and while I think some of their conclusions don't have enough evidence behind them (or only seem to fit well to Western cultures), I do find their descriptions of the cyclical nature of generations to be of value. You don't even need the book for that really... I think the description on this link to Wikipedia gives a sufficient summary of it.