The antonyms for the word "un-matured" are "matured," "ripe," "developed," "grown," "experienced," and "sophisticated." When something is matured, it means that it has reached its full potential and has become fully developed. Ripe refers to something that is ready to be used or consumed, while developed implies that something has been given time to grow and has reached a state of fullness. Grown means that something has increased in size or stature, while experienced suggests that someone has gained knowledge and wisdom from past situations. Finally, sophisticated refers to someone or something that is cultured and refined, having a wide range of knowledge about various subjects.