When Will Federer and the Williams Sisters Call It Quits? Maybe Never.

Advances in physical preparation keep their bodies in the game, and so can the changing nature of sports business and celebrity.

Serena Williams, 40, lost at Wimbledon in the first round for the second consecutive year and will soon face having no ranking in the sport she dominated for decades.Credit...Alberto Pezzali/Associated PressWIMBLEDON, England — Most tennis professionals are retired by their mid-30s. But last week, there was Serena Williams, at almost 41, grinding against a competitor a little more than half her age for more than three hours at Wimbledon.

Venus Williams, too, is here. She played mixed doubles, with tape on her right knee and not so much spring in her step at age 42.…