A person with a developmental disability may be administratively admitted to a facility upon application if the facility director of the facility determines that he is suitable for admission. A person 18 years of age or older, if he has the capacity, or his guardian, if he is authorized by the guardianship order of the Circuit Court, may execute an application for administrative admission. Application may be executed for a person under 18 years of age by his parent, guardian, or person in loco parentis.