Different users of the "Millenial" label start the cohort, by birth year, anywhere between 1976 and 1984 and end it anywhere between 1994 and 2004, with some assigning no end point yet or suggesting a potential later end point than 2004. [0]

Depending on the which of those end points is taken, either all teens, late teens, or no teens are Millenials.

[0] A (probably incomplete) breakdown is available on Wikipedia, https://en.m.wikipedia.org/wiki/Millennials#Date_and_age_ran...