Bill Gates was falling in love with computers.
The Microsoft founder spent his early teens attending the prestigious Lakeside prep school in Seattle. While there, Gates discovered his love of computers by writing a computer code for a version of tic-tac-toe.
Gates and fellow student Paul Allen, his Microsoft cofounder, went into business together for the first time in high school. When Gates was 15, the duo created Traf-O-Data, a tool for tracking traffic flow in the area.
After high school, Gates attended Harvard University but dropped out in 1975 to work full-time on Microsoft, which ultimately made him the world's richest self-made billionaire.
Warren Buffett had multiple revenue streams.
The billionaire CEO of Berkshire Hathaway started building his wealth early. By the time he was 16, he had earned today's equivalent of $53,000, according to the biography "The Snowball: Warren Buffett and the Business of Life" by Alice Schroeder.
One of Buffett's first jobs was delivering The Washington Post. As a teen, he also had several personal business ventures, including selling golf balls, buffing cars, selling stamps, and setting up pinball machines in barbershops.
Oprah Winfrey worked for a local radio station.
Winfrey bounced between family members before moving in with her dad in Nashville, Tennessee, at age 14. The move sparked a drastic change in her life.
Winfrey studied her way to honor-roll status at East Nashville High School and became the most popular girl in her class. More importantly, she established a love for media and joined the school's speech team.
She got her first job when she was 16 as a broadcaster for WVOL, a Nashville radio station. As a 19-year-old sophomore at Tennessee State University, Winfrey got a call from a local television station and left school to start her media career. The gamble paid off.
Mark Zuckerberg was writing computer programs.
Coding was an early hobby of Zuckerberg's. The Facebook founder created a messaging program for his dad's dental office when he was 12.
While enrolled at Phillips Exeter Academy, an exclusive prep school in New Hampshire, Zuckerberg created a music streaming platform that got the attention of AOL and Microsoft. He turned them down.
In his early years at Harvard, Zuckerberg was running Facebook out of his dorm room. He dropped out following his sophomore year to devote his time to the social media platform.
Elon Musk was making his own video games.
The Tesla and SpaceX CEO bought his first computer when he was 10 years old. Two years later, he had written a code for a space-based video game called Blastar. Nothing came of the code until this year, when a Google software engineer turned it into a playable video game.
After graduating from Pretoria Boys High in his home country of South Africa, Musk moved to Canada to attend Queen's University. Following his sophomore year, he transferred to the University of Pennsylvania's Wharton School of Business.
Mark Cuban got his start selling garbage bags.
Cuban, the billionaire owner of the Dallas Mavericks and a "Shark Tank" investor, started his entrepreneurial career when he was 12. He went from door-to-door selling boxes of garbage bags at a profit of $3 per box.
Garbage bags were just the beginning. For extra money, he sold stamps and coins throughout high school. He skipped his senior year to attend the University of Pittsburgh. After his freshman year there, he transferred to Indiana University and used his business savvy to earn money to cover his tuition and rent.
Jeff Bezos spent his summers castrating bulls in Texas.
Between the ages of 4 and 16, the Amazon billionaire spent his summers at his grandparents' ranch in Texas. He did work around the farm like repairing windmills and castrating bulls.
When he wasn't castrating the bulls, he was cooking them as a worker in McDonald's kitchen. Following a rough summer at the hamburger joint, Bezos and his girlfriend started the DREAM Institute, a 10-day educational summer camp for younger kids.
Richard Branson started his first business when he was 17.
In 1968 as a 17-year-old, Branson started a youth-culture magazine called "Student." He sold $8,000 worth of advertising in the first issue.
Two years later, Branson began selling records by mail. This business grew into a brick-and-mortar store and eventually into a recording studio that became known as Virgin Records.
Carl Icahn used poker winnings to pay for college housing.
As a teen, Icahn was admitted to Princeton University but was short on cash. His father was paying his tuition, but he didn't have money for room and board. To solve his financial problems, Icahn got a job as a beach boy in the Rockaways.
The club owners played a regular poker game and invited Icahn to join. After quickly mastering the game, he won about $2,000 each summer, he told Tony Robbins for his book "Money: Master the Game." Today Icahn has an estimated net worth of $24 billion.
Phil Knight was a student athlete.
The Nike founder ran track as a student at Cleveland High School in his hometown of Portland, Oregon. A middle distance runner, he continued his track career at the University of Oregon, which is now known for its flashy and ever-changing Nike football uniforms.
While at Oregon in the late 1950s, Knight and track coach Bill Bowerman shared discontent with the quality of running shoes. In 1964, they founded Nike as Blue Ribbon Sports.
Janet Yellen was her high school's valedictorian.
Yellen, the chair of the US Federal Reserve, was a precocious teenager. During her senior year at Fort Hamilton High School in Brooklyn, New York, she studied math in an honors program at Columbia University.
Yellen graduated in 1963 as valedictorian and was named "class scholar." She was also the editor-in-chief of the school newspaper and decided to interview herself for the story, her former classmate told the New York Times.
