Hedge fund manager Brian Kelly on the future of digital currencies and how to invest in them

Hedge fund manager and author Brian Kelly sat down with CNBC's Mike Santoli to talk about bitcoin. The digital currency was created after the 2009 financial crisis and is now worth more than $1,000 each.

"If you are a baby boomer you buy gold, if you are a millennial you buy bitcoin," said Kelly. "The millennials that I talk to don't trust gold, but do trust math (bitcoin)."

The investor was referring to a 2015 study from Goldman Sachs that showed 63 percent of millennials don't own a credit card and a third said they won't need a bank in five years. Bitcoin will fill the void, Kelly said.

The author of "The Bitcoin Big Bang — How Alternative Currencies are About to Change the World" breaks down the basics of how digital currencies work and explains how investors can get in on the action.

In this exclusive conversation, Kelly, a regular panelist on CNBC's "Fast Money," also shares his views on the U.S. dollar, currency wars, oil, his investment approach and much more.

PRO subscribers can also read the entire transcript of the interview below.