If I were 16 again, I would begin this profitable side hustle, which can generate six figures annually and does not necessitate a degree.

Even billionaires think about starting side hustles.

If Mark Cuban were 16 years old and needed to earn extra money, he would start a specific side hustle in just three steps, as he revealed to CNBC Make It.

He would first learn how to write prompts for AI language models like ChatGPT or Gemini, then teach his friends how to use those prompts on their school papers. Afterward, he would go to small- to medium-sized businesses that are not yet familiar with AI and teach them as well, regardless of his age.

In the U.S., more than half of Gen Zers currently have side hustles, according to a LendingTree report from February. AI prompt engineering, which involves asking chatbots questions to get desired responses, is a particularly lucrative opportunity. The average pay for AI tutors starts at around $30,000 per year, and full-time AI prompt engineers can make up to $129,500, according to ZipRecruiter.

DON'T MISS: The ultimate guide to earning passive income online

To become an AI prompt engineer, you don't need a college degree, but you do need practice and sometimes certifications to understand how large language models work. Some online certification courses, such as those offered by Vanderbilt University or IBM on Coursera, claim you can learn the basics in just one month.

Cuban's imagined side hustle is more advanced than his initial job, which involved selling garage bags door-to-door to his neighbors in Pittsburgh at age 12 to buy a new pair of basketball shoes. He continued to earn extra money as a teenager by selling collectibles like baseball cards, stamps, and coins, which eventually helped him pay for his attendance at Indiana University. There, he worked as a bartender, hosted parties with cover charges, and even picked up work as a dance instructor.

Cuban started his entrepreneurial journey after leaving banking. He sold his first company, MicroSolutions, for $6 million and his second company, Broadcast.com, made him a billionaire when he sold it to Yahoo for $5.7 billion.

According to a Forbes estimate, Cuban's net worth is $5.7 billion. He frequently promotes his online pharmacy, Cost Plus Drugs, which offers affordable prescription drugs by selling them at cost plus a 15% markup.

"During an episode of ABC's "Shark Tank" in 2016, he stated, "I was always a hustler, selling something," and added, "I've always had something going on. That's just my nature.""

Mark Cuban is a panelist on "Shark Tank," which CNBC owns the exclusive off-network cable rights to.

To earn extra money online, sign up for CNBC's course on passive income streams, starting tips, and real-life success stories.