legal age vs eld

legal age and eld both are nouns.

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

As nouns, eld is a hypernym of legal age; that is, eld is a word with a broader meaning than legal age:

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

Other hypernyms of legal age include age.

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