It all depends what you mean by 'oldest', of course. Here are some possibilities:
Oldest garden in Christianity: Garden of Eden
Oldest description of a Buddhist paradise garden: Pure Land of the West
Oldest garden in literature: Epic of Gilgamesh
Oldest domestic outdoor court: Catal Huyuk
Oldest archaeological remains of a temple garden: Temple of Metuhotpe II
Oldest remains of a Chinese garden, maintained for centuries: Tiger Hill (Huqiu Shan)
Oldest space in Europe known to be used for flowers and vegetables: Mycenae
Oldest palace court in Europe: Knossos
Re-creation of the world's oldest garden design in Egypt | Garden ...
Where was the world's first garden made? | Garden Design And ...
The world's first historic gardening experiment | Garden Design ...
These questions lead to a consideration of garden types
