Colorado
Summary: With court approval, an adult between the ages of 18 and 21 may be adopted as a child (child adoption statutes apply).
Most Relevant Colorado Statute:
§ 19-5-201
19-5-201. Who may be adopted.
Upon approval of the court, a person eighteen years of age or older and under twenty-one years of age may be adopted as a child, and all provisions of this part 2 referring to the adoption of a child shall apply to such a person.