The richest people in the world found success at various ages.

Warren Buffett spent over 25 years as a millionaire before becoming a billionaire, while it took Mark Zuckerberg and Jeff Bezos less than two years to graduate to billionaire status.

The richest people in tech averaged five years as millionaires before becoming billionaires.

The richest people in the world have varied origin stories.

Mark Zuckerberg cofounded Facebook in his Harvard dorm room in 2004. By 2007, he was a millionaire. One year later Facebook debuted on the New York Stock Exchange as the biggest tech IPO in history, minting the world's youngest self-made billionaire at the time: 23-year-old Zuckerberg.

Berkshire Hathaway founder Warren Buffett's long-game investing strategies finally cemented his billionaire status at 56 — about 26 years after he first joined the seven-figure club. At age 87, he's now worth nearly $85 billion.

Amazon founder Jeff Bezos was a millionaire for two years before he became a billionaire in 1998, when Amazon went public. At the time, Buffett commanded a fortune of nearly $30 billion. Nearly 20 years later, Bezos is about $30 billion richer than Buffett.

Betway, an online betting site, used Forbes 2018 Billionaire's List and Bloomberg's Billionaire Index to find out how long it took the richest people in the world to go from millionaire to billionaire. The blog looked at when each person first appeared on either list, and also gathered news reports and rankings to pinpoint their age at the time. When it wasn't possible to find an exact age, Betway Insider made an estimate based on the individual's first big success in business.

Tech appears to be the fastest wealth-building industry; the richest people in tech averaged five years as millionaires before becoming billionaires.

Check out the graphic below to see how long it took the richest people in the world to go from millionaire to billionaire. The list excludes two people — Françoise Bettencourt-Meyers and Mukesh Ambani — who both inherited their billions, skipping the millionaire stage completely. All current net worth figures are from Forbes' real-time ranking as of April 4.