When Gertrude Stein said those now famous words to Ernest Hemingway in 1923, she had in mind the writers and artists who came of age during World War I and in the "Roaring Twenties" decade that followed. Besides Hemingway, they included F. Scott Fitzgerald, James Joyce, William Faulkner, and Isadora Duncan.
Of course, Stein's use of "lost" did not mean the war-shattered generation had physically disappeared. Rather, its members were psychologically and emotionally adrift, without purpose, or direction. But for me, her description is also a lament for members my own American generation who were born between 1930 and 1939; many of whom currently live on Sanibel and Captiva.