This study investigates the genetic architecture of biological age (BAG) across nine human organ systems—brain, eye, cardiovascular, hepatic, immune, metabolic, musculoskeletal, pulmonary, and renal—using data from 377,028 participants of European ancestry from the UK Biobank. The BAGs were calculated using cross-validated support vector machines, incorporating imaging, physical traits, and physiological measures. The study identifies 393 genomic loci linked to the BAGs in each organ system, demonstrating both organ specificity and interorgan connections. Genetic correlation analyses show that the genetic correlation between BAGs mirrors their phenotypic correlation, supporting Cheverud’s Conjecture. Mendelian randomization analyses reveal potential causal relationships between chronic diseases, lifestyle factors, and the BAGs. The findings highlight the complex and interconnected nature of biological aging and provide insights into potential interventions for improving organ health.This study investigates the genetic architecture of biological age (BAG) across nine human organ systems—brain, eye, cardiovascular, hepatic, immune, metabolic, musculoskeletal, pulmonary, and renal—using data from 377,028 participants of European ancestry from the UK Biobank. The BAGs were calculated using cross-validated support vector machines, incorporating imaging, physical traits, and physiological measures. The study identifies 393 genomic loci linked to the BAGs in each organ system, demonstrating both organ specificity and interorgan connections. Genetic correlation analyses show that the genetic correlation between BAGs mirrors their phenotypic correlation, supporting Cheverud’s Conjecture. Mendelian randomization analyses reveal potential causal relationships between chronic diseases, lifestyle factors, and the BAGs. The findings highlight the complex and interconnected nature of biological aging and provide insights into potential interventions for improving organ health.