Here's what Warren Buffett said when Tony Robbins asked him how he got so rich

Everyone has to start somewhere, even the wealthiest, most successful people.

Billionaire Warren Buffett hasn't always been as incredibly rich as he is today - in fact, 99% of his wealth was earned after his 50th birthday.

The investing legend has been slowly building his fortune over the years, and today, the 85-year-old billionaire is one of the richest men in the world, with an estimated net worth of over $60 billion.

How did he come to earn such a mind-blowing amount of money?

Motivational speaker and author of "MONEY: Master The Game," Tony Robbins, decided to ask him.

"I asked Warren Buffett - I said, 'What made you the wealthiest man in the world?'" he tells entrepreneur and business coach Lewis Howes in an episode of his podcast,"The School of Greatness."

"And he smiled at me and said, 'Three things: Living in America for the great opportunities, having good genes so I lived a long time, and compound interest."

Buffett has always been an advocate of keeping things simple and focusing on the long-term - that's why he recommends low-cost index funds.

One of the keys to Buffett's wealth is simply time - 60 plus years of smart investing has allowed him to reap the benefits of compound interest.

Compound interest is when the interest earned on your investments earns interest itself - it's what causes wealth to rapidly snowball, and in Buffett's case, snowball to billions and billions of dollars.