young vs old

young and old both are nouns.

Word	Noun	Adjective	Verb	Adverb
young	Yes	Yes	No	No
old	Yes	Yes	No	No

young (noun)	old (noun)
any immature animal	past times
young people collectively

young (adjective)	old (adjective)
(used of living things especially persons) in an early period of life or development or growth	of long duration; not new
(of crops) harvested at an early stage of development; before complete maturity	(used especially of persons) having lived for a relatively long time or attained a specific age
not tried or tested by experience	skilled through long experience
being in its early stage	(used for emphasis) very familiar
suggestive of youth; vigorous and fresh	excellent
	just preceding something else in time or order
	belonging to some prior time