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

Nauru

Article 84 states that citizens of Nauru can vote for members of Parliament and for referendums based on the principles of universal suffrage. The voting age in Nauru is 20 years old. (Constitute Project, “Nauru’s Constitution of 1968 with Amendments through 2015”).

Voting Rights and Suffrage · Country sources (all rights) · Years mentioned: 1968, 2015 · Last edited 2022-12-28 · Edit on GitHub