The Wisdom Economy – Part 3: Reservoirs of Wisdom explores a new framework for understanding ageing populations as reservoirs of accumulated knowledge, experience, judgment, mentorship, resilience, and cultural memory. Moving beyond narratives of dependency and decline, this article argues that humanity's greatest untapped wealth may already exist within older generations. As societies confront demographic transformation, the challenge is no longer simply extending life, but transforming longevity into legacy by recognizing, preserving, and mobilizing wisdom for future generations.