This study examined the semantics of query reformulations in relation to age and task difficulty. Task difficulty was manipulated using a metric called task preciseness defined as the semantic similarity of the task description with the content of the target page(s) containing the answer. A behavioral experiment was conducted in which 24 younger adults and 21 older adults solved six low precise and six high precise information search tasks. The behavioral outcomes were found to be in line with preceding work indicating that the metric was successful in differentiating different levels of task difficulty. Analysis of the semantic relevance of queries showed that for low precise tasks, the queries generated by younger adults had significantly higher mean semantic relevance than that of older adults whereas for high precise tasks, it was the other way round. When analyzed across reformulations, it was found that the mean semantic relevance of queries generated by older adults, decreased for both low and high precise tasks. For younger adults, it remained constant for high precise tasks and even increased for low precise tasks. Implications of these findings for the design of information search systems are discussed.