At 88, Berkshire Hathaway chairman and CEO Warren Buffett is worth around $84.2 billion, according to Forbes. Nicknamed the "Oracle of Omaha" thanks to his Midas touch within the stock market, Buffett's tenure as an investor started almost eight decades ago.

"The year was 1942, I was 11, and I went all in, investing $114.75 I had begun accumulating at age 6," Buffett wrote in his annual letter to shareholders, published on Saturday. "What I bought was three shares of Cities Service preferred stock. I had become a capitalist, and it felt good."

Cities Service was a natural gas company founded in 1910, but no longer exists. Buffett calculated what his $114.75 would be worth today had he invested the money in a no-fee S&P 500 index fund with all of its dividends reinvested instead. (It's important to note that the first index fund was not available until 1975.)

Based on that, his stake would have been worth (pre-tax) $606,811 on Jan. 31, 2019, Buffett wrote in his letter.

"That is a gain of 5,288 for one. Meanwhile, a $1 million investment by a tax-free institution of that time — say, a pension fund or college endowment — would have grown to about $5.3 billion," Buffett added.