Kenyan
The proper adjective for Kenya is "Kenyan." It is used to describe anything related to the country, such as its culture, people, and geography. For example, you might refer to Kenyan cuisine or Kenyan wildlife.
Kentuckian is the proper adjective for Kentucky.
The proper adjective for southwest is "southwestern."
The proper adjective is Haitian.
The proper adjective for Portuguese is "Portuguese."
Vietnamese is the proper adjective for Vietnam.
No, old is not a proper adjective. A proper adjective is an adjective derived from a proper noun, such as Swiss cheese, Bolivian pottery, Chinese silk, etc.
The proper adjective for Georgia is Georgian.
The proper adjective for George is Georgian.
Freudian is the proper adjective for Freud.
Mayan is itself a proper adjective.
The proper adjective for Siam is Siamese.