September 23: Argentine Juan Martin del Potro, the 2009 US Open champion, turns 24. Currently ranked No. 8 in the world, he has been ranked as high as fourth. He defeated Roger Federer for the 2009 US Open title, breaking the Swiss's five-year run as champion. He missed nearly the entire 2010 season with a wrist injury, but reached the quarterfinals at the Australian Open in 2012 and won the bronze medal at the 2012 Summer Olympics in London.
Seventeen-time Grand Slam doubles winner Mark Woodforde is 47. The Australian teamed with countryman Todd Woodbridge to win 11 men's doubles titles, although his first came with American John McEnroe at the 1989 US Open. Woodforde won 67 men's doubles titles including Wimbledon six times (five straight from 1993-1997), the Australian Open twice, the US Open thrice and the French Open once. In mixed doubles, he won the Australian Open twice and the other three majors one time each. He and Woodbridge also combined to win gold in men's doubles at the 1996 Olympic Games and the silver at the 2000 Sydney games.
September 26: Current US Open, Wimbledon and Olympic defending champion Serena Williams turns 31. Williams has amassed 30 total Grand Slams -- 15 in singles, 13 in women's doubles and two in mixed doubles. Among her singles Grand Slams are five each at the Australian Open and Wimbledon, four at the US Open and one at the French. She has also completed the career Golden Slam in women's doubles, with three gold medals (200, 2008, 2012), five WImbledon crowns, four Australian Open titles, and two each at the US and French Opens. In mixed doubles, she won both Wimbledon and the US Open in 1998 and has reached the finals of the Australian Open and the French Open.
September 28: The WTA's senior member, Japan's Kimiko Date-Krumm, turns 42. Date-Krumm has had a truly unique career, retiring from tennis at age 26 after competing in the 1996 Summer Olympics, then returning to the sport 12 years later at age 38. She has been ranked as high as No. 4 in the world, and reached at least the quarterfinals of all four Grand Slam tournaments, winning a total of eight WTA titles.
Croatian ATP player Marin Cilic turns 24. Currently ranked No. 13 in the world, Cilic has been as high as No. 9 following a trip to the Australian Open semifinals in 2010. He has also reached the quarterfinals of the US Open twice, including this year, and has won eight ATP-level tournaments.