Tell him it's internet money, and he could have bought a Bitcoin for one cent seven years ago, then sold it for more than $1100 less than five years later.
Tell him it went up in value more than 5.5 times in 27 days during November 2013.
Tell him if he had bought $10 worth of Bitcoins at the start of November 2013 he could have sold his stash for $55 at the end of November 2013.