Although hearing loss accounts for much of the difficulty older adults have comprehending spoken language, cognitive factors also play a role. There is evidence that, relative to younger listeners, older listeners have more difficulty recognizing a word when it has many lexical competitors, but little is known about the time course of lexical competition in older adults. We monitored the eye movements of sixteen young adults (18-30 years) and sixteen older adults (60-80 years) as they followed spoken instructions to click on objects displayed on a computer screen. We manipulated the lexical frequencies of the target word and the phonologically similar competitor. Older listeners were more likely than younger listeners to fixate competitors during comprehension only when the competitor was high frequency. Simulations using a model of spoken word recognition suggest that these age differences may arise from a combination of differences in the effect of frequency and competitor inhibition.