They may be young, but the following seven people had the vision and drive to turn themselves into billionaires before they reached the ripe "old" age of forty.

1. Yusaku Maezawa: from rock star to mega-rich retailer by age 35

Yusaku Maezawa

Yusaku Maezawa is a former rock musician who started selling CDs and band t-shirts online back in the early 1990's. He then started a company called Start Today, along with a wildly-successful e-commerce site called Zozotown. Zozotown is set up like a mall, with different shops for different types of fashion and other products that are all sold on consignment.