Adoption, at the core of everything is a legally binding process, in which a family unit is born and one or more adults agree to take parental custody of a child and its well-being. However, sometimes the adoption process involves the adoption of adults by fellow adults. So to speak.
Adult adoption is that of adopting someone over the age of 18. Some states are more strict than others, but in every case the adopter will need legal consent from the adoptee to finalize the adoption. An adult may opt to be adopted at 18 if he or she became a legal adult before he or she was available for adoption in the foster care system. It is also sometimes done for legal purposes, particularly to secure inheritance. Some adult adoptees may also choose to be adopted by their birth parents after a successful search and reunion.
Some states have their own exceptions to the adult adoption: Michigan and Nebraska do not allow adult adoption. In Arizona, the adult has to be under 21. Alabama only allows adult with severe disabilities to be adopted. Ohio only allows adults who have established a relationship via foster or stepparent or those with severe mental and physical disabilities to be adopted after their 18th birthday. Foreign adult adoption is less lenient of a process and should be evaluated on a case basis.