Tennis player Madison Keys both young and wise heading into U.S. Open

Madison Keys is ranked in the top 10 in the world, a Grand Slam semifinalist who just played for an Olympic bronze medal and has earned career prize money of well over $4 million.
She’s also only 21, much closer in age to her middle school days than to No. 1 Serena Williams, and the youngest woman in the top 20 by nearly a year-and-a-half.
This is where the American finds herself as she heads into next week’s U.S. Open: an established pro with the game to win major titles, yet compet