Aim Simultaneous performances of motor and attention‐demanding tasks are common in activities of everyday life. The present cross‐sectional study examined the changes and age‐related differences on mobility performance with an additional cognitive or motor task, and evaluated the relative dual‐task cost (DTC) on the motor performance in young, middle‐aged and older women. Methods A total of 30 young (mean age 25.12 ± 3.00 years), 30 middle‐aged (mean age 47.82 ± 5.06 years) and 30 older women (mean age 72.74 ± 5.95 years) were recruited. Participants carried out: (i) single task: Timed Up & Go Test; (ii) cognitive dual‐task: Timed Up & Go Test while counting backwards by three; (iii) manual dual‐task: Timed Up & Go Test while carrying a glass of water. A repeated measures anova with between‐factor as age groups and within‐factor as tasks was carried out to assess the effect of aging on the performance of mobility tasks. DTC was calculated as ([performance in single‐task − performance in dual‐task] / performance in single task) × 100%. One‐way ancova were carried out to compare the DTC among the three age groups. Results A significant interaction between age groups and task (F4,172 = 6.716, P < 0.001, partial η2 = 0.135) was observed. Specifically, older women showed a worse mobility performance under dual‐task condition compared with young and middle‐aged groups. Furthermore, DTC differences in cognitive task were observed in older women compared with younger and middle‐aged women (F2,86 = 7.649, P < 0.001, partial η2 = 0.151), but not in manual task. Conclusion Dual‐task conditions might affect mobility performance differently across the lifespan, and could be particularly challenging in older women. Geriatr Gerontol Int 2017; 17: 315–321.