legal age vs majority

legal age and majority both are nouns.

Word	Noun	Adjective	Verb	Adverb
legal age	Yes	No	No	No
majority	Yes	No	No	No

As nouns, legal age and majority are synonyms defined as:

legal age and majority: the age at which persons are considered competent to manage their own affairs

legal age (noun)	majority (noun)
the age at which persons are considered competent to manage their own affairs	the property resulting from being or relating to the greater in number of two parts; the main part
	(elections) more than half of the votes
	the age at which persons are considered competent to manage their own affairs