Understanding the mechanical properties of the aging thorax is important in the development of restraint systems to protect the older population. This study investigated how the material properties of costal cartilage change with age. Indentation testing was used to study the material properties of human costal cartilage. Ribcages were obtained from 11 human subjects ranging in age from 23 to 77 years. Costal cartilage from the second, third, and fourth left ribs were excised and prepared into 6 mm thick cross sections. The cross sections were tested using spherical indentation with a ramp-hold relaxation test. Shear and elastic moduli were calculated from the stress relaxation response. The results showed only a slight trend of increasing costal cartilage stiffness with age and there was a larger overall standard deviation in the older specimen values. Differences were observed during specimen preparation which included changes in color, increasing inhomogeneity, and varying regions of calcification. Calcification was observed as shells surrounding the softer cartilage, as well as calcified strata running transversely through the interior of the cartilage. These regions should affect the overall mechanical response during thoracic loading, but were not as apparent in the results of the current study because the indentation area was localized near the center of the cartilage cross sections.