Madison Keys has the serve of a polished veteran, has achieved things in tennis many of her older contemporaries will never match, and turned pro all the way back in 2009. She's been on the tour for eight years—more than a third of her entire life.
Serena Williams owns the greatest serve in women's tennis history, has won more Grand Slam singles titles than anyone in the Open era, and turned pro in 1995—she's been on tour for more than half of her life.
So you can understand Williams' reaction on Snapchat after hearing Keys say, "I am a veteran now" on Tennis Channel: