Women become increasingly sedentary with age, therefore it is important to understand women’s barriers and motivators to physical activity (PA) at different ages to optimize PA interventions. However, limited studies have examined differences in perceived barriers to PA between young and middle-aged adult females. This study investigated barriers and motivators to PA in young (18–35 years, n = 94) and middle-aged (36–55 years, n = 77) women in England, using the International Physical Activity Questionnaire and the Exercise Benefits Barrier Scale, administered online. Mean scores for total, subscale and individual barrier and motivation items were reported for each age group. Independent t-tests assessed age group differences in total scores. A MANOVA explored age group differences in subscale scores. Total barrier and motivator scores for the whole group were M = 2.04, SD = 0.45 and M = 3.20, SD = 0.44, respectively. No age group differences were observed in total scores (p > .05). The leading barrier to PA in both groups was physical exertion, which was rated significantly higher by the young cohort (M = 2.70, SD = 0.59), compared to the middle-aged cohort (M = 2.43, SD = 0.60). Motivator subscales were ranked in the same order for both groups (physical performance, psychological outlook, preventive health, life enhancement, and social interaction), with no age group differences in scores. PA promotion strategies for young and middle-aged women should focus on improving multiple aspects of physical performance and support the development of self-regulatory skills such as strategic planning, goal setting, self-monitoring, and time-management.