Adopting an Adult adult adoption n. The adoption of a person over the age of majority (as defined in State law). Adult adoption was quite a common occurrence during the ancient/classical periods to carry on a dynasty, occupation, or family name; to care for a parent in old age; or to protect property rights. Today, however, there are three main reasons people pursue the adoption of an adult person. Inheritance. This is the most common reason for adult adoption, creating a parent-child relationship that will be legally recognized so that the adopted person can inherit from the adoptive parent(s). Formalizing...