The antonyms for the word "unmatured" are "mature," "developed," "ripened," "grown-up," and "adult." These words imply a state of physical, emotional and intellectual advancement that is absent in the term "unmatured." Mature implies a full or finished state, demonstrating an individual's preparedness to handle exigencies. Developed indicates growth, advancement, or progress. Ripened connotes the process of maturation, reaching perfection, and fullness of flavor. Grown-up suggests a progression from childhood to adulthood, indicating a sense of responsibility, independence, and self-sufficiency. Adult suggests full maturity or attainment of a certain age, bringing with it added privileges and responsibilities.