We count whole calendar years and months first, then whatever's left over becomes days — the same way you'd count by hand on a calendar, so it correctly handles different month lengths and leap years.
Generation labels are approximate and vary slightly by source: Gen Alpha (2013–2025), Gen Z (1997–2012), Millennials (1981–1996), Gen X (1965–1980), Baby Boomers (1946–1964), Silent Generation (1928–1945).
Yes — it uses the proleptic Gregorian calendar (today's calendar projected backward), which is the standard way to compute this, though it may not match historical calendars actually in use in some countries before their Gregorian adoption date.