Objectives <p>Older adults' autonomy is frequently undermined by well-intentioned but paternalistic caregiving, representing a pervasive form of benevolent ageism. This research examines the long-term physical health consequences of such autonomy restrictions and investigates whether the endorsement of infantilizing age stereotypes serves as an underlying psychological mechanism.</p> Methods <p>Study 1 analyzed 10-year longitudinal data (2008–2018) from the Chinese Longitudinal Healthy Longevity Survey using a progressive analytic strategy: a random-intercept cross-lagged panel model (1a, <i>N</i> = 4,288), panel data regression with instrumental variables (1b, <i>N</i> = 3,909), and Cox proportional hazard regression (1c, <i>N</i> = 12,053). Study 2 (<i>N</i> = 154) experimentally primed older adults with either undermined or preserved autonomy to assess the causal impact on stereotype endorsement and subsequent cognitive and physical performance.</p> Findings <p>After controlling for baseline health and covariates, Study 1 demonstrated that undermined autonomy independently predicted poorer self-rated health and increased mortality risk over time. Study 2 revealed that exposure to autonomy-undermining cues heightened older adults' endorsement of infantilizing stereotypes, which in turn impaired their physical performance.</p> Conclusions <p>Undermined autonomy poses a significant independent threat to older adults' physical health and longevity. This detrimental effect is partly driven by the internalization of negative stereotypes regarding older adults' competence. Findings underscore the critical need to protect older adults' autonomy and challenge the infantilizing attitudes that often rationalize paternalistic practices.</p>