IIRC, Strauss and Howe had it as 1961-1981 in "Generations", so it would make sense that you'd be in the border regions. Ultimately, where the border is set may depend in part on what's used as the defining moment for the Millennials. Probably the role that either 9/11 or the Great Recession played in their early adulthood, if I had to guess. (There might be a provisional case for adult/not-adult on 9/11 as the divider, though I'm not sure if that should be 18, 21, or some other number.)