Younger mothers are less likely to continue breastfeeding compared with older mothers. However, few studies have explored this finding. The aim of this study was to investigate breastfeeding initiation and duration among women aged under 25 and 25 years or older, and assess the extent to which any differences associated with maternal age were explained by other factors. Methods: All women who gave birth in September and October 2007 in two Australian states were mailed questionnaires 6 months after the birth. Women were asked about infant feeding, maternity care experiences, sociodemographic characteristics, and exposure to stressful life events and social health issues. We examined the association between maternal age, breastfeeding initiation, and breastfeeding at 6 months, while adjusting for a range of social and obstetric risk factors. Results: While younger women were just as likely to initiate breastfeeding as older women (AdjOR 1.13; 95 CI 0.63-2.05), they had almost twice the odds of not breastfeeding at 6 months (AdjOR 1.76; 95 CI 1.34-2.33). Several psychosocial factors may explain why young women are less likely to breastfeed for longer periods. Conclusions: Given the complexity of young childbearing women s lives, supporting them to breastfeed will require a multisectorial approach that addresses social disadvantage and resulting health inequalities.