I've seen a number of divergent dates set up for generation cut-offs, and even some that break the various generations into smaller sub-categories based on whether one is born earlier or later in the range provided. There's about a 2-3 year gray area as far as the transition from Baby Boomers to Generation X, but all of them tend to include 1980 (the year of my birth) as either the cut-off or close to he cut-off for when Gen X becomes Gen Y. This probably explains why in terms of my taste in music, art and even cultural figures that I admired, I usually ended up either looking back to the early 90s and 80s (I technically came of age in the mid 1990s), or was otherwise fixed on things at the present that were a throwback to said time period, whereas my sister who was only born a couple years later did not gravitate towards those things.
On-topic:
I'm a bit skeptical of Bush dropping out of the race, but I don't think he has been guaranteed the nomination by the party. He's been doing absolutely terrible in both the debates and all of his campaign appearances and while I'm not predicting he will drop out before Iowa, if he does it won't surprise me. The person who will benefit most from him dropping out will be Rubio, so there is probably some benefit in him staying in until after Iowa as the optics of him splitting the establishment vote will give Paul a clearer path to a potential victory there if things turn around, which I think they will.