He isn't enamored with how Robinhood pools orders from individual investors and sells the data to big Wall Street trading houses such as Citadel Securities. Last year Robinhood paid a $65 million fine to the pre-Gensler SEC for misleading customers about this source of revenue—which is called payment for order flow and has been around longer than many of Robinhood's 18 million customers, whose median age is 31. Payment for order flow made up 75% of Robinhood's revenue last year, and it's why the firm can offer commission-free trades.