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

Czech Republic

According to Chapter I, Article 56, all citizens at the age of 18 years or older have a right to direct and universal voting. Under Chapter 2, this voting is done by secret ballot and is based on proportional representation. (Constitute Project, “Czech Republic’s Constitution of 1993 with revisions through 2013).

Voting Rights and Suffrage · Country sources (all rights) · Years mentioned: 1993, 2013 · Last edited 2022-12-28 · Edit on GitHub