Compared to other sports, tennis is still for the young

— -- MELBOURNE -- Peyton Manning will quarterback the Denver Broncos in the AFC championship this weekend, two months shy of his 40th birthday. His counterpart will be New England Patriots quarterback Tom Brady, who is 38 years old.

Asked about playing at that age, Maria Sharapova replied, "Do I see myself playing at 38 as a quarterback? Not as a quarterback. I definitely don't see myself -- oh, my goodness. I just compared myself to a quarterback. Is that a compliment? Or not?

"I definitely don't see myself playing at 38.''

The question is, what pro tennis players do play singles at 38 and beyond?

Meanwhile, there is only one player in the Australian Open older than 36 -- Radek Stepanek, who at 37 was trying to become the oldest man to reach the third round of a Grand Slam since Jimmy Connors did so in the 1991 US Open at 39. Venus Williams was the oldest woman here at 35. Then there is Lleyton Hewitt, who is playing his final tournament here before retiring at age 34. Flavia Pennetta, who won the US Open last year, is not here because she retired after winning in New York at age 33 -- which still was older than Marion Bartoli, who won Wimbledon in 2013 and retired a month later at age 29.

Tennis players are getting older, with the average age increasing significantly -- roughly four years -- since 2002. No teenager has won a Grand Slam since Sharapova won the 2006 US Open at age 19. There are only four teens in the ATP top 100 and five in the WTA 100. Meanwhile, there are 34 men in the ATP top 100 who are 30 years old or older. There are 13 women in the WTA top 100 in their 30s. And as Serena Williams and Roger Federer, both 34, clearly show, some players are still dominating at later ages (though Federer hasn't won a major since turning 31).

Yet tennis players still are several years shy of lasting as long as, say, Bartolo Colon, who pitched in the World Series last fall at 42 -- and he was one of at least eight major leaguers in their forties last season. Despite the advances in age, there are only two male players older than 34 -- Victor Estrella Burgos at 35, and Ivo Karlovic at 36 -- in the ATP top 100 (Stepanek is ranked No. 188) and three women in the WTA top 100 who are 34 or older.

Hey, everyone's body starts breaking down as we enter our 30s and beyond. Aging is part of life. But why is it that more athletes seem to keep going longer in other sports than in tennis?

"I don't know the reason for that," Serena said. "I think tennis is a sport that really beats your body. Then you start at such a young age, train for so many years. You're so consistent with that training for hours and hours a day. Then you do physical training. It's actually a lot that goes into tennis."

The oldest tennis player to win a major in the Open Era was Ken Rosewall, who won the 1972 Australian Open at 37. Serena is the oldest woman to win a major, at age 33 and nine months last year -- though she has a very good chance of extending that record. Gordie Howe, meanwhile, played hockey until he was 52. Jamie Moyer was still pitching in the major leagues at age 49. George Foreman won the heavyweight championship at age 45. Roger Clemens won a Cy Young at age 42.

"I think the reason tennis players usually can't play in their mid- or late 30s is tennis is a sport based on very quick, explosive movement, unlike, for example, a quarterback in football or a pitcher in baseball," Patrick McEnroe said. "Obviously, there are other things for a quarterback -- they have to move a little, and a lot of it is brain power in addition to their skill -- but they don't have to move as often or as quickly. And for a pitcher, it's just about your arm.

"In basketball, it can depend on what position you play. I don't think you see too many point guards playing into their late 30s or 40s. You see some bigger guys because their mobility isn't as important."

Quickness certainly fades faster than endurance in athletes.

Pam Shriver, who played the 1978 U.S. Open at age 16 and retired in 1996, said part of it is that tennis players' pro careers also start earlier in tennis -- Serena played her first pro tournament at age 14 -- so it's more of a grind on the body.

"We also have two seasons almost. It's an 11-month season,'' Shriver said. "You really have to manage it smarter than ever. So you have to be really smart in how you pace yourself. Those are the two main things. Your career starts earlier, and your seasons are longer."

On top of that, tennis players also have far more demanding travel schedules.

"I'm not taking anything away from those guys in other sports by any means, but everything is done for them,'' Steve Johnson said. "Whereas, next week, I'll fly home for a couple days, then fly on to Memphis, Delray, Acapulco and maybe back here to Australia for Davis Cup. Then to Indian Wells, then Miami. Then Monte Carlo and back home. Then Europe and home. Then Europe and home [again]. It's a little tougher on the body, just in terms of travel."

Bethanie Mattek-Sands, who played on five continents last year, said the schedule demands and the desire to be with family play a significant part in it.

"I know I'm not getting hit by a 300-pound guy, but in football, they play one game a week and they know their schedule for the whole year," said Mattek-Sands, who is a big football fan and whose husband, Justin, played football in college. "When they travel, everything is taken care of for them. They probably even have somebody wake you up in the morning. They may even carry you some place."

Another big difference, Shriver said, "is in football, you have 10 other guys surrounding you, OK? And you're not on the field half the time. In tennis, you're playing offense and defense. And you're it. Those are huge differences."

Indeed, having teammates who can take care of many responsibilities plays a significant role. As does being able to sit in the dugout for 10 to 15 minutes every inning.

"For a tennis player, it's not only about an agility and general movement issue, it's also a singular sport," McEnroe said. "The other sports, you can go from being a star player as a basketball player to being an important sixth or seventh man coming off the bench and hitting a couple shots, so you can prolong your career doing that. Kobe Bryant is still playing, but he's not nearly the player that he was. He still is a somewhat valuable asset to his team over the years.

"But in tennis, if you lose half a step, you're pretty much done, even if you're a great player."

Stepanek, by the way, lost in straight sets to Stan Wawrinka on Thursday. But he plans to keep going.

"As long as the hardware is ready, I will continue playing,'' he said. "I love this game and I am still competing with the best ones so I don't know where better I can be.''