Advanced maternal age at childbirth (AMAC) is increasingly common, yet its long-term association with frailty remains unclear. Using three longitudinal cohorts (CHARLS, KLoSA, and HRS; N = 21,090), we examined this association via Cox proportional hazards models and mediation analysis. After multivariable adjustment, AMAC (≥35 years) was associated with increased frailty risk in the Chinese (hazard ratio [HR]: 1.21, 95% confidence interval [CI]: 1.03–1.42) and Korean (HR: 1.24, 95% CI: 1.02–1.50) cohorts, while AMAC (≥40 years) showed a similar direction in the United States cohort. Life satisfaction partially mediated this association, accounting for 8.9% of the total effect in KLoSA and 22.4% in HRS, with substantial attenuation of the direct effect in CHARLS. These cross-national findings indicate that psychosocial well-being may represent a modifiable pathway for frailty prevention among women with a history of AMAC.