Guillaume Apollinaire
Two years after being wounded in World War I, Apollinaire died in the Spanish flu pandemic of 1918; he was 38.
Paul Valéry
Valéry is best known as a poet, and he is sometimes considered to be the last of the French symbolists. However, he published fewer than a hundred poems, and none of them drew much attention. On the night of 4 October 1892, during a heavy storm, Paul Valéry underwent an existential crisis, an event that made a huge impact on his writing career. Eventually, around 1898, he quit writing altogether, publishing not a word for nearly twenty years. This hiatus was in part due to the death of his mentor, Stéphane Mallarmé. When, in 1917, he finally broke his 'great silence' with the publication of "La Jeune Parque"; he was forty-six years of age.