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

Thailand

Article 95 of the Thai Constitution grants Thai citizens of 5 years or more that are registered and are at least 18 years old the right to vote. Article 85 states that members of the House of Representatives of Thailand are elected via direct suffrage by secret ballot. (Constitute Project, “Thailand’s Constitution of 2017”).

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