Once and for all. Each generation is 18 years. Boomers begin at the end of WW2 is the point of reference.
1946-1963: Boomers
1964-1981: Gen X
1982-1999: Gen Y / millenials
2000-2017: Gen Z / doomers
Each can be subdivided into 3 tiers of 6 years: older, middle, younger.
18 is perfect because it is the age of majority in most places, it is superdivisible, and it makes consistent generations lengths.