What is the oldest written source in this country that mentions this right?

Seychelles

Under article 24 of the Constitution of Seychelles all citizens over the age of 18 have the right to be registered as a voter as well as to participate in public affairs and run for office. Both the President and members of the National Assembly are elected into office. (Constitute Project, “Seychelles’s Constitution of 1993 with Amendments through 2017”).

Voting Rights and Suffrage · Country sources (all rights) · Years mentioned: 1993, 2017 · Last edited 2022-12-28 · Edit on GitHub