The present study investigated the role of cognitive flexibility and vocabulary abilities in explaining age-related differences in information searching with a search engine. Nineteen older and 20 younger participants had to carry out nine searches and to complete a battery of cognitive tests. Older participants obtained poorer search performance with fewer correct answers, and lower task completion speed. They interacted little with the system, and showed specific difficulties in getting out of impasses and reformulating unfruitful requests. Regression analyses suggested that age differences in the number of requests were moderated by differences in cognitive flexibility and that the older participants did not leverage their increased vocabulary in producing new keywords. The findings suggest that the age-related decline in cognitive flexibility plays a role in the age-related differences observed in searching for information, especially in the way users get out of impasses. The results have implications for designing search engine tools. Copyright © 2010 John Wiley & Sons, Ltd.