While gender itself has little to do with how early or late a child becomes fully toilet-trained, the tendency of toddler and preschool boys to be active physically may delay their training somewhat. Two large population studies show that males are delayed by approximately 6 months compared to girls in toilet training. Population studies, however, are not always representative of individuals. Still, other factors—such as a desire for self-mastery or a desire to please the parent—may overcome such physical issues. The difference in timing between genders is less important than individual factors that are more influential on a child's readiness for toilet training.
Additional Information from HealthyChildren.org: