immature

Synonyms: adolescent baby babyish callow childish crude green half-grown imperfect infantile infantine jejune juvenile kid kidstuff premature puerile raw sophomoric tender tenderfoot underdeveloped undergrown undeveloped unfinished unfledged unformed unripe unseasonable unseasoned unsophisticated untimely wet behind ears youthful

Antonyms: adult developed experienced grown mature old