IMMATURE

[adjective] [disapproving] - childish; unable to be or act as calmly and wisely as people expect you to, at the age you have reachedStop being so silly and immature, Derek!She's rather immature for her age, don't you think?She's politically immature (= has had little experience of politics).(specialized) If something is described as immature it can also mean that it is not yet completely grown or developed.While the animals are still immature, they do not breed.