G.K., 20, resides in the Los Angeles area. On a recent Sunday, the college student clicked on an app where he maintains an account and claims to have risked $250 on two NFL games, the same amount on a pair from Major League Baseball, and smaller sums on props.

His activity is legal even though California prohibits sports betting and, of states that allow regulated betting, all but four have set the minimum age at 21.

Under current law, what G.K. does between classes and homework is not considered wagering.