Earlier this year, Serena Williams, 31, became the oldest woman to hold the No. 1 ranking in the history of the WTA.
Williams turned pro in 1995, just shy of her 14th birthday.
In the late 1990s, Williams battled a number of teen stars, including her sister Venus Williams and Martina Hingis. Many of the top veterans in the game were themselves former teen stars.
The Williams sisters, Jennifer Capriati, Hingis, Chris Evert, Tracy Austin and Steffi Graf all won Grand Slams before they were 20.
In the 1990s, teenagers won 15 Grand Slams. That number fell to three in the 2000s.
Today, there are no teenagers among the WTA's Top 20. In fact, there are more 30-year-olds in the Top 50 than teenagers.
What happened? Why has the teenage phenom become a rarity in women's tennis?