With the rise of age-friendly digital tools, older adults increasingly access health information online. Yet weakened gatekeeping in digital media has facilitated the spread of health rumors. Corrective efforts sometimes backfire, reinforcing belief in misinformation—a phenomenon known as the backfire effect. This study explores its formation among older adults via semi-structured interviews with 22 participants. Using grounded theory and integrating the Stressor–Strain–Outcome (SSO) framework with the Elaboration Likelihood Model (ELM), it identifies two pathways: worldview and familiarity backfire effects. Findings reveal how cognitive dissonance, emotional defense, and individual traits shape resistance to corrections. The study proposes targeted strategies involving message design, social communication, psychological inoculation, and digital literacy. It offers insights into improving health misinformation correction for aging populations.