Answer:
An adult can definitely adopt an adult. This can prove to be one of the easiest adoptions. Simply because the adult being adopted would need no permission from his or her biological parents as long as he is over the age of 18. If that adult is married, is the only permission needed. The spouse will need to give his/her permission for you to be adopted. I have heard of several forms of adoption but adult adoption I've heard to be the easiest.