Most folks – yes. By your definition Donald Trump is a millennial because… wait for it… he was born before the turn of the… waaaaaait for it… millennium.

Language often evolves in seemingly unintuitive ways (e.g. lunch), there's no "corrupt in our cultural conscious" going on. Someone born in the early 80s is going to have much less in common (especially in terms of technology) with someone born in the late 90s. By 1997 the oldest millennials were starting to have kids who would very clearly not belong under the heading "millennial".