young person vs spring chicken

young person and spring chicken both are nouns.

Word	Noun	Adjective	Verb	Adverb
young person	Yes	No	No	No
spring chicken	Yes	No	No	No

As nouns, young person and spring chicken are synonyms defined as:

young person and spring chicken: a young person (especially a young man or boy)

Other synonyms of young person include younker, youth.

young person (noun)	spring chicken (noun)
a young person (especially a young man or boy)	a young chicken having tender meat
	a young person (especially a young man or boy)