There are two critical, real and large factors, IMHO, that basically boil down to common experiences only appreciated by those who lived them. It is actually something my wife and I discussed in our very first conversation, in wotmania chat, because it is also why age differences matter less with age. Do you remember where you when the Berlin Wall fell? For anyone too young to drink in the US the answer is "nowhere," a fact of life that makes our worldview and theirs radically different: The "evil empire" I grew up treating as given never existed for them.

By the time they enter their late 20s, people born five years apart can usually point to mostly the same iconic moments in their respective lives; when the difference rises to ten, twenty or more years, it takes much longer for that to be true. For you and I, Watergate and the Kennedy assassination are history; we do not relate to them in the same way or on the same level as people who remember them first hand, and cannot conceive the pre-1963 world in which they lived. We keep hearing that "911 changed everything," but that is true of every paradigm shifting event (which is what shifts the paradigm.)

That said, it is not as simple as Generation A begetting Generation B which begets Generation C, etc. My wife is a little over seven years younger than I, which makes her (IIRC) only a couple years older than you: Are the two of you from MY generation, or the one young enough to be my kids? Your ages are about equidistant from both, meaning we share many experiences unknown to those 20 and below (e.g. Challenger and the Berlin Wall) but some pivotal events I recall (e.g. the Iranian hostage crisis and Reagan shooting) are also unknown to ya'll. The experiences of those born at the start of the Baby Boom (such as my mom) are not identical to those born a decade or more later (such as the eldest of her brothers,) and assuming otherwise inaccurately oversimplifies matters more complex than simply checking a number on a birth certificate.

That difference is recognized in the designation of younger Boomers as Generation Jones, a demographic in many ways as distinct from its elder siblings and their children as it is from its own children and parents. Generation Jones became rebellious as it neared adulthood, in a conscious repudiation of the order its elder siblings took for granted and its parents considered dearly bought, yet both prized. I find generational evaluations that incorporate such intergenerational epochs more useful, in part because the nature of reproduction makes any baby boom/bust likely to be followed by another 20-30 years later. This graph illustrates that somewhat (and puts the most (in)famous baby boom in perspective; it looks more like a DROP in births after the Great War, with birth rates unsurprisingly rising about the time children born in the previous relative boom reached childbearing age.) Contraception, higher professional priorites and different levels of prosperity reduced the magnitude, yet after Baby Boom reproduction levels began falling it later rose again for nearly a decade--about the time the first wave of Baby Boomers hit their mid-twenties.

Those of a given "generation" born a decade apart have significantly different experiences, and that complicates the impact of shared experiences among people of the same age, because the largest and longest influence on most people is their parents. As you have already alluded to, people born on the same day will share and remember all the same paradigm shifting events, but if one was born to twenty year old parents and the other to thirty-five year old parents, they will still view those same events through different lenses. Most folks I grew up with remember "The Day After," Iran-Contra, Glasnost and the Berlin Wall as well as I do, but their hippie parents had different outlooks, expectations and households than mine. My friends fathers were in the age group that burned its draft cards, but being five years old when Japan bombed Pearl Harbor, and entering the Navy just after Korea, made MY father less inclined to call the US military "baby-killers," and more sympathetic to Southeast Asian wars. If I sired my first child tomorrow it would probably have a rather different take on the same events viewed by others of its generation sire by 25 year olds born when their parents were 25; my father was a grown man the day their grandparents were born, and that will inevitably impact the perspective each of us gives our children, which will in turn color the way those children view the same events. My mothers youngest brother once teased me about being a "Gen Xer" in her hearing, prompting her to observe that since he is only eight years younger than I (and thus 22 years younger than her) any comments about "my" generation apply equally to him; once again, you and he are of different generations, but I could be considered a member of either or both.

Thus I both agree and disagree with your contention here. I DO think generationalism is a valid and powerful phenomenon because shared experiences, both their own and their parents, tend to link each generation in a way that seperates them from others. However, I contend that a given generation does not directly give rise to the next, but the one following the next. I also contend that factor further complicates dynamics that already made neat convenient divisions between generations impossible based solely on birthdates. The distinction is valid, important and instructive, but not nearly as simple as lables like "Boomer" or "Gen Xer."