Universal adult suffrage is just oligarchy of another sort, since "universal" and "adult" are mutually exclusive terms here. The Greek had certain limitations on who can vote; we today have limitations of our own liking. If we want standards of democracy that would stand the test of time (something desirable in a discussion involving both history and pseudo-future), we probably have to consider absolutely universal vote where criminals, infants, lunatics and people-in-potentia have their say, too.
Timo Saloniemi