Bill Gates says he only felt successful at 42, decade after becoming world’s youngest billionaire

"I wouldn’t say that I felt comfortable that we were successful until about 1998 or so," Gates told CNBC Make It. That was 11 years after he took Microsoft public and became the youngest billionaire at the time at age 31.

He went on to hold the title of the world’s richest man for 13 consecutive years, from 1995 to 2007. Now 69, Gates has a net worth estimated by Forbes at $107 billion, ranking him 14th among America’s wealthiest individuals, his first time outside the top 10 in 34 years.

Tech billionaire Bill Gates. Photo courtesy of Gates' Facebook

In his memoir "Source Code", released earlier this year, Gates described working 80-hour weeks writing software while constantly fearing Microsoft could lose its position in the personal computer revolution.

He said his anxiety over Microsoft’s future often kept him from enjoying its success. Even after taking the company public in 1986 and appearing on the cover of Fortune, he avoided celebrating milestones, fearing complacency.

"I was always running scared," he said. "So whenever Microsoft would [celebrate] anniversaries, I’d be like, ‘I have no time to look backwards.’"

It was not until the late-1990s that he finally felt more secure. "Wow, we can even make a few mistakes and still be OK," he recalled. "I thought I was one mistake away from death until then. That was just my mentality."

At that time, Microsoft had become the world’s most valuable public company, worth more than $250 billion, while Gates’s personal wealth reached $58 billion, according to CNBC.

"That’s the first time I look back and say, ‘OK, we are in a pretty good position here, and I understand why my competitors are so jealous that they think they need the Justice Department to help them out,’" he said.

Gates also credited Microsoft’s rise to his early passion for coding, recalling how at 13 he would sneak out of the house to write and test computer code until 2 a.m, as reported by Fortune. That streak continued into college, when he left Harvard University in 1973 to launch Microsoft.