That makes no sense at all. Generation X/Y/Z, sure (except does it roll over after Z and would that be AA or just A?). But millennial? The name implies turn-of-the-millennium, not before as that would be a premillennial. Back in the day, there were reports of people trying to plan a "millennium baby" to be born in the first week of the year 2000 so it would make sense to call them millennials as they're not exactly babies any more.