Falls in older adults often occur during everyday walking activities, especially those with complex mediolateral demands. How muscle coordination is modulated to achieve these complex mediolateral demands and how age-related changes in modulation may compromise this ability are unknown. This study investigates age-related changes in the complexity of muscle coordination during a goal-directed lateral stepping task using electromyography and motor module analysis. Twenty-nine older adults (OA) and twenty-six younger adults (YA) performed habitual treadmill walking and a goal-directed lateral stepping task designed to mirror real-world tasks with increased lateral movement demands. Muscle coordination complexity was quantified using the variability accounted for by one motor module, with higher values indicating reduced complexity. Both YA and OA exhibited reduced muscle coordination complexity in the stance leg during precision stepping compared to habitual treadmill walking. This reduction was larger for OA and associated with worse walking balance. In contrast, muscle coordination complexity was not different across conditions in the stepping leg for either age group. The results of this study provide insights into age-related differences in how muscle coordination complexity is modulated to meet goal-directed lateral stepping demands during walking that may help explain increased susceptibility to falls in older adults.