emerging adult

Noun

 * 1)  In some conceptions of human life phases, a member of the subset of adults who, although postadolescent (having passed the age of majority), retain some aspects of mental or emotional immaturity.

Usage notes
Not consistently and clearly differentiated from young adults; sometimes asserted to be not adult, usually in muddled ways that do not then also precisely define when or how adulthood begins, do not offer any coordinate term (whether full-fledged adult or otherwise), and do not accord with legal definitions of adulthood.