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

Guatemala

There are two provisions for privacy protection in the 1985 Guatemalan Constitution. Article 23 grants privacy in the home (vivienda) and Article 24 protects correspondence and other documents (Constitute Project, “Guatemala 1985 rev. 1993”).

https://constituteproject.org/constitution/Guatemala_1993?lang=en

Privacy Rights · Country sources (all rights) · Years mentioned: 1985, 1993 · Last edited 2022-12-28 · Edit on GitHub