Background: Associations between individual socioeconomic indicators and biological aging leave open whether the pattern extends across social origin, attained education, and economic resources. I examined these aspects of socioeconomic position and educational mobility in relation to Klemera-Doubal method (KDM) age acceleration across 12 countries in the Survey of Health, Ageing and Retirement in Europe (SHARE), and whether cross-country variation in these associations followed a welfare-state or economic-development pattern. Methods: Using SHARE Wave 6 (2015), I constructed three sex-specific KDM measures from overlapping biomarker panels in 10,043-14,015 adults aged 50-75 years and followed outcomes through Wave 9. Predictive validity was assessed for ADL/IADL limitations, cognition, and mortality. Survey-weighted models estimated pooled SES associations and tested country heterogeneity; exploratory analyses summarized multidimensional country profiles and examined six national indicators. Results: All three KDM measures were prospectively associated with incident functional limitation, lower cognition, and mortality; ADL/IADL odds ratios ranged from 1.29-1.61 and mortality hazard ratios from 1.44-1.92. Across all 21 pooled coefficients, greater socioeconomic advantage was associated with lower KDM age acceleration; each of the six specification-level tests had a false-discovery-rate-adjusted P