Based on the thread in US politics.
Three people alive to-day were eligible to vote in 1920 but since all were black women then residing in the South, it seems unlikely any of them did. Based upon this list (
http://en.wikipedia.org/wiki/List_of_oldest_living_people), it seems that several other women alive to-day were eligible to vote in 1924 of whom at least some were presumably white and/or resided outside the South indicating that this election was the earliest one at least in the United States.