Bill Gates isn't sure he would've become a billionaire if he'd grown up like kids today, dealing with the distractions of smartphones and social media.

Gates, the co-founder and ex-CEO of Microsoft, helped make computers and the internet ubiquitous. But he might never have built the tech giant — valued at $3.26 trillion, as of Wednesday afternoon — without the time he spent growing up roaming around with friends, exploring the outside world, and reading and thinking deeply in his room for hours at a time, Gates wrote in a blog post on Tuesday.

"When I felt restless or bored — or got in trouble for misbehaving — I would disappear into my room and lose myself in books or ideas, often for hours without interruption," Gates wrote. "This ability to turn idle time into deep thinking and learning became a fundamental part of who I am."

He added: "It was also crucial to my success later on."

In his blog post, Gates recommended a book: "The Anxious Generation," by New York University social psychologist Jonathan Haidt, which explores how smartphones and social media have "rewired" kids' brains.

The book also argues that these technologies helped create a youth mental health crisis, marked by rising levels of loneliness and depression for Gen Zers. Constant use of smartphones and social media can also negatively affect young people's memory, ability to concentrate and attention spans, research shows.

Gates touted his "play-based childhood" — which inspires creative thinking, research shows — over the "phone-based childhood" that many kids today experience, according to Haidt's book.

"Our attention spans are like muscles, and the non-stop interruptions and addictive nature of social media make it incredibly difficult for them to develop," Gates wrote.

Committing to 'uninterrupted concentration'

Throughout his career, Gates has frequently credited his success to his voracious reading habit and ability to self-isolate.

In the 1990s, the then-Microsoft CEO would even retreat to an isolated cabin in the wilderness "with nothing but a big bag of books and technical papers" for what he called his annual "Think Week," he wrote in his blog post. Those periods found Gates "committed to uninterrupted concentration" — he wouldn't even check his email — so he could "read, think, and write about the future" without interruption, he added.

It's a smart idea, productivity expert Laura Stack told CNBC Make It in 2019.

"We must create an environment that gives us the ability to focus our minds without interruption from coworkers, spouses, children, pets and technology, or we'll never be able to concentrate on higher-order activities," Stack said.

Gates' weeks of intense focus helped spur big ideas, including Microsoft's development of the Internet Explorer browser, according to The Wall Street Journal. Now, the technologies Gates and Microsoft helped popularize risk preventing the deep thinking that people need to spur similar innovations, according to the billionaire.

"Without the ability to focus intensely and follow an idea wherever it leads, the world could miss out on breakthroughs that come from putting your mind to something and keeping it there, even when the dopamine hit of a quick distraction is one click away," wrote Gates.

Want to make extra money outside of your day job? Sign up for CNBC's online course How to Earn Passive Income Online to learn about common passive income streams, tips to get started and real-life success stories.

Plus, sign up for CNBC Make It's newsletter to get tips and tricks for success at work, with money and in life.