Answer:
Time-shifting the Generations
First, a question of timing. The whole notion of generations came about due to the work of two sociologists – William Strauss and Neil Howe, in the 1991 book Generations. They argued that if you looked at the variations in birth rate from the founding of the country to the present, there are clear patterns showing rises and declines with a cycle of about 18 years. The Baby Boom generation was the 23rd generation after the country was founded by their reckoning, making them Generation W.
There’s a much more complex attempt at building a whole framework about Turnings and Saecular centuries (that old four score and ten) much of which gets into far more dubious territory. However, I believe that the basic observatiton about generations being unique is probably correct, but only if you fix an assumption that I think was flawed in their initial work. Strauss and Howe treated as a generation as being from the mid-point to the mid-point of birth rate.