David Karp dropped out of a high profile high school in New York at the ripe young age of 15. As it turns out, that worked out pretty well for Karp as he went on to start Tumblr, the very popular social media/blogging site, which he later sold to Yahoo! For $1.1 billion. Yes billion, with a b. At the age of 23, Karp will never have to work another day in his life whereas most people at his age are trying to figure out how to pay off their student loans.