Opinion: Watching Serena’s US Open defeat was a stinging reminder of my own age and ambition

I stress-watched the US Open women's final on Saturday between Serena Williams and Bianca Andreescu, frantically texting friends at every missed first serve and line-call challenge. Watching Serena, something the world has done collectively since she won her first Grand Slam title in 1999, has been more than just a spectator sport. It has been a live-action study in women's ambition, and how it changes -- or doesn't -- over time.