Maternal age at first childbirth has increased in most developed countries in the past 20 years. The purpose of this study is to investigate effects of maternal age at delivery and parity on successful initiation of exclusive breastfeeding (EBF). This retrospective study investigated 1193 singleton dyads with vaginal-delivered at 37–42 gestational weeks during January and December in 2011 at one large “Baby-Friendly” certified hospital in Japan. A multivariate logistic regression model was used to evaluate individual and combined effects of maternal age and parity on successful initiation of EBF after adjusted for pre-pregnancy body mass index, gestational weight gain, pregnancy complications, mothers' underlying illness, smoking and alcohol drinking habits, gestational week at delivery, child's sex and nurturing support from grandparents. Success rates of EBF at one month after child delivery was 69.4% in primiparous aged ≥ 35 (group A: n = 284), 73.5% in multiparous aged ≥ 35 (group B: n = 268), 74.3% in primiparous aged < 35 (group C: n = 432), and 82.3% in multiparous aged < 35 (group D: n = 209). Older maternal age and primiparous became independently associated with EBF initiation. The combined effect for successful initiation of EBF was the lowest in group A referent to group D both at discharge and at one month (odds ratio (OR) 5.9, 95% confidence interval (CI): 3.0–11.9, and OR 2.2, 95% CI: 1.4–3.4, respectively). Primiparous mothers in late child-bearing aged 35 years or older are at the greatest risk of EBF initiation.