Patrick Collison and John Collison

When brothers John and Patrick Collison founded and sold their auction and marketplace management system Auctomatic for $5 million in 2007, John was 17; his older brother 19. In 2009 they founded online payment processor Stripe, John dropped out of Harvard, and the brothers moved to Silicon Valley (yes, the comparisons to Mark Zuckerberg’s path to founding Facebook have been made). Now Stripe, which allows companies to process payments in 100 global currencies – including Bitcoin – with just a few lines of code, has a $5 billion valuation; it counts Elon Musk, Peter Thiel and Visa and American Express as investors; and fellow 40 Under 40 companies Kickstarter, Lyft, and Instacart as customers. Next up for Stripe: ramping up hiring. The company expects to add another 200 employees in the next three months, bringing its head count to 500.

For more on Stripe, read “A billion-dollar startup earns its stripes.”