Roger Federer is old. That's the simple explanation for why he has fallen off so dramatically this year.
At 32, he is currently the 23rd oldest player in the top 100, the sixth oldest player in the top 50, the second oldest player in the top 25, and the oldest player in the top 10.
While tennis players generally stick around longer than they used to, there are only a handful of men over the age of 33 on tour.
Pro tennis is increasingly a sport that requires impeccable physical conditioning. There are currently zero under-20 players in the top 100, and only one over the age of 35.
Federer has entered the final chapter of his career. He's struggling through nagging injuries (a back injury gave him fits this summer), losing to no-name qualifiers at small tournaments, and getting his doors blown off before the quarterfinals in majors.
He still might have another run at a major left in him.
Agassi won the Australian Open at age 32, and Sampras won his last major at age 31. But those guys didn't have all-time great players like Nadal, Djokovic, and (if we're being generous) Murray to deal with.
In short, Federer's days of sustained success without the possibility of a letdown are over.
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