While most teens spend their youth honing work skills in entry-level jobs, whether that’s slinging fast food or working retail, others get that spark to succeed at an early age. There’s no shortage of useful advice out there to help even the very young make strong business decisions. There is also no minimum age to become a millionaire, as these “kids” know firsthand. From playing the stock market to starting up their own companies, check out these 40 teens who made millions before turning 20.