Cody Berman's first entrepreneurial venture was a disc golf manufacturing company he started with a friend at 19. The business was not a financial home run, the now 30-year-old told Business Insider, but it taught him skills he would use for years: "I learned how to market, how to network, how manufacturing works, how to talk to customers, build websites." Over the next decade, Berman kept experimenting. The Massachusetts-based serial entrepreneur, author of " Retire by 30 ," and host of " The