A chest model was generated to represent the rib cortical bone material property and thickness of a 70-year-old person. The chest model was applied to THUMS V4.1 occupant models in four body sizes:​ midsize male, small female, large male and overweight female. Frontal collision simulations were performed to predict rib fracture risks using three-specification restraint systems with different restraining balances for the shoulder belt and airbag. Simulation results show that higher Body Mass Index, rather than sex difference, is related to a higher number of rib fractures in elderly occupants of the driver’s seat. The contact force from shoulder belt to anterior chest was greater than that from the airbag and was one of the possible factors causing rib fractures. The load limiter of the seat belt reduced the contact force to the chest, but it allowed further head forward displacement. The study results indicate that the combination of low load limiter and early airbag constraint was effective for elderly occupants with various body types.