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

Russia

Article 81 states that the President is elected every 6 years via universal, equal, and direct suffrage by a secret ballot. The voting age in Russia is 18 years of age. (Constitute Project, “ Russia’s Constitution of 1993 with Amendments through 2014”).

Voting Rights and Suffrage · Country sources (all rights) · Years mentioned: 1993, 2014 · Last edited 2022-12-28 · Edit on GitHub