youth vs spring chicken

youth and spring chicken both are nouns.

Word	Noun	Adjective	Verb	Adverb
youth	Yes	No	No	No
spring chicken	Yes	No	No	No

As nouns, youth and spring chicken are synonyms defined as:

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

Other synonyms of youth include young person, younker.

youth (noun)	spring chicken (noun)
the freshness and vitality characteristic of a young person	a young chicken having tender meat
young people collectively	a young person (especially a young man or boy)
a young person (especially a young man or boy)
early maturity; the state of being young or immature or inexperienced
the time of life between childhood and maturity
an early period of development