You're right about the age of Snow White, but things aren't always that rosy for Disney. When they made a film from Kipling's The Jungle Book, that book was 73 years old. If Walt (who took strong personal interest in the project) felt comfortable making money by adapting a work that old to a new medium, why shouldn't I feel comfortable adapting his even older older works?
(Yes, this is a Tu Quoque argument)