Abstract Selective attention is involved in multiple daily activities. Several authors state that it experiences a decline after 20 years, although there is no agreement regarding the cognitive processes that explain it. Two theories dominate the discussion: The theory of inhibitory inefficiency and the theory of processing speed. At the same time, it has been suggested that there could be complementary relations between both; however, it is not clear what the contribution of inhibition and processing speed is on the changes of selective attention. Therefore, the present study proposes to analyze this contribution, in adults between 20 and 80 years old. To assess selective attention and inhibitory control, two indices of a visual search task were obtained in which participants must identify a target stimulus among a set of distracting stimuli. To evaluate the processing speed, a response speed task was used. The main results indicate that, from the age of 60, a gradual decrease in selective attention begins and that this decline can be largely explained by a decrease in processing speed and inhibitory control. We discuss about the literature on the development of selective attention, the contribution of processing speed, and the inhibitory inefficiency hypothesis.