Professional tennis is older than it's ever been

Roger Federer of Switzerland
Clive Brunskill | Getty Images

Serena Williams' victory aside, the big surprise at this year's Australian Open was that it's a throwback to a much earlier time.

Names that had once belonged to a previous generation of tennis stars cracked the finals, like Venus Williams, Rafael Nadal (age 30) and Roger Federer (age 35). However, the dirty little secret is: Tennis players on average have been getting older in the past several years.

In 2016, men's Grand Slam tournaments had an average age of 27.7 years, the eldest its been in the Association of Tennis Professionals' history. Serbia's Novak Djokovic, who won the French and Australian opens and went to the final of the U.S. Open, turned 29 last May. He lost the in New York to Stan Wawrinka, Switzerland's 31-year-old star.

It wasn't just the finalists in the men's and women's brackets. Thirty-somethings took up many of the semifinal and quarterfinal spots at the Australian Open last year, including Wawrinka and Jo-Wilfred Tsonga on the men's side.

This year's Aussie Open women's bracket saw both Williams sisters (Serena is 35 and Venus is 36), along with Croatia's Mirjana Lucic-Baroni—who first broke onto the professional scene a full 20 years ago in 1997.

So while this weekend's winners are both in their 30s, it's not just them. The rest of the competition is all getting older—but still winning.