The variability of walking gait timing increases with age and is strongly related to fall risk. The purpose of the study was to examine the interaction of age, cognitive function, and gait performance during dual-task walking. Forty-two, healthy men and women, 50-80 years old, completed the Mini-Mental State Exam (MMSE) and Trail Making Test (TMT) to assess cognitive performance and were separated into groups by decade of life. They then performed dual-task walking, at a self-selected pace, on an instrumented treadmill during three cognitive loading conditions: (1) no cognitive load, (2) subtraction from 100 by 1s, and (3) subtraction from 100 by 3s. The treadmill recorded spatiotemporal gait parameters that were used to calculate the mean and coefficient of variation for each variable over ten strides. Time to complete the TMT was positively correlated with age, stride time, double-limb support time, and mediolateral instability and was inversely correlated with single-limb support time. Subjects in their 70s increased their stride time and double-limb support time during the most challenging dual-task condition (subtraction by 3s), whereas subjects in their 50s and 60s did not. Across conditions, the variability of stride length, stride time, and single-limb support time was greatest in the 70s. Mediolateral instability increased only for subjects in their 70s in the subtraction by 3s condition. Reduced cognitive function with age makes it difficult for older adults to maintain a normal, rhythmical gait pattern while performing a cognitive task, which may place them at greater risk for falling.