Tennis legends Billie Jean King and Gardnar Mulloy celebrated milestone birthdays on Friday. King is celebrating her 70th birthday; Mulloy celebrates his 100th birthday.

King is one of the founders of the WTA tour and over the years has become one of the world's most influential advocates for women’s rights. She won 39 Grand Slam titles, including 12 singles, 16 doubles, and 11 mixed doubles crowns.

Mulloy is the first International Tennis Hall of Fame inductee to reach the century mark. He began playing tennis at age 11 in Miami.

"I played [American] football and baseball in the city, before my father got me into tennis," Mulloy told ATPWorldTour.com. "Eventually, we won the U.S. National Father & Sons’ title three times. I enjoyed competing, but when I grew up it was considered a ‘sissy’ sport in the United States.”

Mulloy added that he does not believe that today’s players are better than ones from the past.

“That’s nonsense,” he said. “Racquets, tennis balls and equipment development has changed the sport. But tennis ball covering is very thin now. Prior to World War II, the inner core was made of pure grey rubber, but due to the wartime demand for rubber, manufacturers substituted a black synthetic rubber substance and made the core thinner. It made the tennis ball faster in play, and, as we have seen over the past two decades, the number of players going to the net has decreased.

“If former generations—players such as Bill Tilden, Bobby Riggs, Jack Kramer and Rod Laver competed with the same equipment against the likes of [Rafael] Nadal, [Novak] Djokovic, [Andy] Murray and [Roger] Federer, they would still dominate at every tournament."