[mrrrgn]

As the namesake suggests, "millenials" are ideally people who were young-adults around the 00's. That generally means born from the early/mid 80's to mid-90's.

Gen z were/are young adults during the '10s. Gen alpha will be young adults during the '20s.

Generally a person's pre-teen/teen/early 20's are very formative so the shared experiences that a generation will have probably do form a real connective tissue within the age cohort that separates them from those with different experiences. A binary (anyone less than x years old is a y) isn't so useful to describe such a phenomenon.

[excalibur]

Generations are supposed to be longer than 10 years.

https://en.wikipedia.org/wiki/Generation

[mrrrgn]

https://en.wikipedia.org/wiki/Millennials

1982 - 1996, that is more than ten years. But the people in that range would have shared formative experiences during the '00s. Thus the moniker millenials.