Processing speed, inhibitory control and working memory have been identified as the main possible culprits of age-related cognitive decline. This article describes a study of their interrelationships and dependence on age, including exploration of whether any of them mediates between age and the others. We carried out a LISREL analysis of the performance of 79 participants of low educational level aged 40-91 years in six cognitive tasks. In the best mediational model the effects of age on inhibitory control and working memory are largely mediated by its effect on processing speed. However, in the best-fitting model age has only direct effects on processing speed, working memory, and inhibitory control. (Contains 3 tables and 2 figures.)