Retired French-American tennis player Mary Pierce has expressed her admiration of the WTA stars who continue to stretch their careers longer and longer, most notably including Venus and Serena Williams.

For Mary Pierce, in women’s tennis, age is only a number.

Although she isn’t planning a comeback of her own, the former world No. 3 and two-time Grand Slam winner, who turned 40 earlier this year, appreciates the courage of women who have kept up with the game.

“To me, age doesn’t matter at all,” Pierce told Wimbledon.com in an exclusive interview at the WTA Finals in Singapore.

“If you’re happy with the level that you’re competing at, then go for it. As long as you’re healthy and as long as you’re loving it and hungry and want to work hard and fight, then keep doing it,” she said.

Pierce, started an early carrier, having made her first appearance at the WTA tournament at the age of 14 and having an early taste of victory, as she won her first singles trophy at 16 in 1991, she has applauded the performance of older players in the game. Admitting that the WTA’s age eligibility clause limits the number of tournament players can compete in before the age of 18.

“I think that’s partly why we’re seeing older players be more successful, too,” she said, “But with advances in technology and science, there are always new and better ways that you can take care of yourself and train better.”

Pierce moved herself back into the top 5 at the age of 30, finishing as runner-up at the French and US Opens when she made a mini-comeback of her own in 2005.

She has said her best days had been when she was 30, and could work hard and feel really alive. Unfortunately, she was compelled to retire, following a knee injury in the autumn of 2006.