Webster's Revised Unabridged Dictionary · 1913

Lawful

Lawful , adjective

1.
Conformable to law; allowed by law; legitimate; competent.
2.
Constituted or authorized by law; rightful; as, the lawful owner of lands.
Collocations (1)
Lawful age , the age when the law recognizes one's right of independent action; majority; -- generally the age of twenty-one years. Also called legal age or age of majority.

In some of the States, and for some purposes, a woman attains lawful age at eighteen. Abbott.