immature vs junior

immature is not a noun while junior is a noun.

Word	Noun	Adjective	Verb	Adverb
immature	No	Yes	No	No
junior	Yes	Yes	No	No

immature (noun)	junior (noun)
	the younger of two persons
	a third-year undergraduate
	term of address for a disrespectful and annoying male

immature (adjective)	junior (adjective)
not yet mature	younger; lower in rank; shorter in length of tenure or service
characteristic of a lack of maturity	used of the third or next to final year in United States high school or college
(used of living things especially persons) in an early period of life or development or growth	including or intended for youthful persons
(of birds) not yet having developed feathers
not fully developed or mature; not ripe