The purpose of this study was to investigate the cognitive and non-cognitive determinants of age-related decline in a deductive reasoning task, and to examine their relative contributions to task performance. A sample of participants aged between 60- and 98-years old were tested. The results showed that all the measures accounted for age-related variance in reasoning, and mainly showed the significance of environmental variables on reasoning abilities of old people and their interactions with cognitive capacity of working memory and speed of information processing.