He read Nietzsche and Kant in high school, when not making excellent model airplanes.
Have you read Kant?
He does not long to go back among the French who, according to Heine, now drink beer and read 'Fischte' and Kant.
Around the mid-nineties, Parfit started reading Kant.
During the 1920s Heidegger read Kant extensively.
Reinhold's letters were widely read and made Kant the most famous philosopher of his era.
Such are the Baileys; such, to take their great prototype, was Herbert Spencer (who couldn't read Kant); such are whole regiments of prominent and entirely self-satisfied contemporaries.
He read Stefan Zweig, Emerson, Kant, Schiller and Goethe.
Einstein once said that you should be able to explain scientific concepts to a schoolchild, but forgot that when he was a schoolchild he was charging through university math books and reading Kant.