age vs legal age

age and legal age both are nouns.

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

As nouns, legal age is a hyponym of age; that is, legal age is a word with a more specific, narrower meaning than age:

age: a time of life (usually defined in years) at which some particular qualification or power arises
legal age: the age at which persons are considered competent to manage their own affairs

Other hyponyms of age include age of consent, majority, minority, nonage, drinking age, voting age.

age (noun)	legal age (noun)
how long something has existed	the age at which persons are considered competent to manage their own affairs
a time of life (usually defined in years) at which some particular qualification or power arises
a late time of life
an era of history having some distinctive feature
a prolonged period of time