From page 752, of Laitz's The Complete Musician 4th edit.
''(...) By continuing the process of stacking thirds, these composers added another third above the seventh, creating a ninth chord; by adding another third above that ninth they created an eleventh chord(...)''
These composers=generally late 19th and early 20th century composers (Bartok,Ravel,Debussy,Schoenberg)
From the text I draw on the conclusion that 9th chord invented during those years which surprised me as I though that it is much older than 1900s.
Is it the thing that the author mentions or is it something else? When in the western music history, 9th chords invented and widely used first?