Can an adult of age 23 be adopted?

Yes, adults can indeed be adopted but some states may limit the cirucmstances in which that may iccur.  It is my understanding that the state of Alabama does indeed set a limit in those matters.  It is my undertsanding that Alabama only allows adults over the age of 18 who are permanently disabled or mentally retarded to be adopted. Good luck.

And, in further clarification of the answer provided by another attorney, since this question appeared in the Immigration Law section, I will presume that your question about adoption somehow relates to immigration benefits as a result of the adoption.  For immigration purposes, a person has to be adopted before the age of 16 in order to qualify for immigration benefits from his/her adoptive parents.