Mark Twain once said “age is an issue of mind over matter. If you don’t mind, it doesn’t matter.” The unfortunate reality for most athletes is that the years do take a toll, and the body gives up before the mind. Yet there are rare individuals who defy the perceived limitations of age and prove the amazing capacity of the human body. Some showed incredible durability in their own sport, while others reinvented themselves by taking on new challenges when many thought they were done. Here are 20 athletes who pushed the limits of what we thought was possible, and proved that age doesn’t always matter so much after all.

Herschel Walker

In the 1980’s Walker was a physical freak of a running back who could bowl over NFL defenders. In the 2010’s, Walker is a physical freak and mixed martial artist who could tear off your arms in the ring. He’s claimed to do 1000 pushups and 3000 situps every day, and seriously considered an NFL comeback at age 50.

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Dara Torres

A swimming prodigy, Torres started racing internationally at the age of 14. She won 12 Olympic medals in three different decades, including three silver medals at the 2008 games in Beijing, when she was 41. And she reportedly will attempt to make her sixth Olympic team later this summer, at the 2012 U.S. Olympic Team Trials – Swimming, in Omaha from June 25 – July 2.

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Julio Franco

Franco played professional baseball for a quarter century. He ended his Major League Baseball career with a .298 batting average, but also logged hits in several other leagues, including the Mexican League, Japan’s Nippon Professional Baseball, the Dominican Winter League, and South Korea’s Korean Baseball Organization. He’s been reported to eat as many egg whites in a week as you’ll eat all year.

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Brandi Chastain

Perhaps no sports bra in history has been as commented on, debated, and discussed as the one Chastain spontaneously flashed after scoring the winning penalty kick for the U.S. in the 1999 World Cup. She played on the US national team from 1988 until 2004. Despite a history of knee injuries, in 2008 Chastain took on and completed the New York City Marathon at age 40.

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Nicklas Lidstrom

At 41 years old, Lidstrom is the oldest active player in the NHL, and he remains one of the better players in the league. From 2001 to 2011, he had a lock on the Norris Trophy (given to the game’s best defenseman), winning the award seven times. He’s been a member of four Stanley Cup-winning teams, and represented his native Sweden in the past four Olympic Games.

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Nancy Lopez

Lopez started playing golf when she was 8 years old, won the New Mexico Women’s Amateur at age 12, and turned pro after her sophomore year of college. Her professional career spanned more than 30 years, during which she won 48 LPGA titles and three major championships. She also racked up more than $5 million in tour winnings.

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Karch Kiraly

Kiraly is synonymous with beach volleyball. He is the winningest player in AVP history, and a three-time Olympic Gold medal winner, competing in at least 28 pro seasons and claiming a title in 24. But his accomplishments didn’t happen only in the sand. Playing indoor volleyball, Kiraly led his college team, the UCLA Bruins, to three NCAA national championships (in 1979, 1981 and 1982) and won two Olympic Gold Medals for the USA. He would go on to win a third at the 1996 games, the first time Beach Volleball was an Olympic event.

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Sheryl Swoopes

In 1997 Swoopes was the first-ever player drafted into the WNBA, and still played in the league during the 2011 season, when she was 40 years old. By that time, she had been named the league’s MVP three times (2000, 2002 and 2005), was the leading vote-getter in All-Star balloting five times (1999, 2000, 2002, 2003 and 2005), and earned most valuable player honors in the 2005 All-Star game.

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Emmitt Smith

From his 15-year career, Smith is the NFL’s all-time leading rusher (18,355 yards) and one of its most prolific scorers (164 touchdowns). He won three Super Bowl rings with the Dallas Cowboys. After retiring from professional football, he went on to win “Dancing With the Stars.”

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Martina Navratilova

Talk about longevity: Navratilova, a tennis legend, won 59 Grand Slam titles during her career, including her final Grand Slam victory at age 49. Her 344 tournament victories are unrivaled, and her nine Wimbledon singles championships are a record.

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Lance Armstrong

Clearly, we’re a little biased when it comes to Armstrong, but let’s look at the facts: More Tour de France wins than anyone else in history. After his first retirement, he took to marathon running and finished the New York City Marathon in 2 hours and 46 minutes. He then unretired, returned to the Tour and finished on the podium. Today, at 40 years old, he’s taking a shot at triathlons, with his sights set on the Ironman World Championships in Kona this fall.

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Jeannie Longo

If any cyclist has been even more dominant in France than our patriarch, it’s Longo. She’s a 15-time French national road champion, 10 time national Time Trial champion, and remains a force on the bike at 53 years old.

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George Foreman

When Foreman won his first major title - an Olympic Gold Medal at the 1968 Summer Olympics in Mexico City - The Beatles “Hey Jude” was the number one song in America. When he won Boxing’s Heavyweight Title for the last time, the top Billboard song was “The Sign” by Ace of Base and it was 1994. Foreman boxed professionally until he was 48 years old, winning 76 matches during that time, including 68 knockouts.

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Joan Benoit Samuelson

Samuelson, or “Joanie” as she’s known in the running world, came out of relative obscurity to win the Boston Marathon in 1979. She went on to become the first-ever Olympic Gold Medalist in the marathon, winning the inaugural event at the 1984 Summer Games in Los Angeles. Joanie remained competitive in the years since, qualifying for seven Olympic Marathon Team Trials, and celebrated her 50th birthday by finishing the 2008 Trials in Boston by running a sub-2:50 marathon.

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Gordie Howe

At 51 years old, following an eight year retirement, Howe returned to the NHL and played in all 80 regular season games, scoring 15 goals. He’d later return to the ice in 1997 and complete a shift for in the IHL (a minor league in hockey), when he was nearly 70 years old. That made Howe the only man ever to play professional hockey in six different decades (1940s – 1990s).

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Bruce Matthews and Clay Matthews, Jr.

Both of the Matthews brothers played 19 seasons in the NFL, with Clay (#57, above) spending his years with two teams (Cleveland Browns and Atlanta Falcons) while Bruce spent his entire career with the Houston Oilers/Tennessee Titans. Bruce never missed a game due to injury and earned 14 Pro Bowl nominations, including one at age 40, while Clay became the oldest player ever to record a sack when he did so at age 40 years, 282 days.

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Cynthia Cooper-Dyke

Another WNBA star who was still ballin’ at 40, Cooper is a four-time world champion – and a teammate of Swoopes. Cooper spent years playing in European leagues before the formation of the WNBA. Once professional basketball came to the U.S., Cooper-Dyke helped make the Houston Comets a dynasty.

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Jamie Moyer

Moyer is an example of why patience (and perseverance) pays off. The durable lefty reached the World Series at age 45, when he played for the Philadelphia Phillies (one of seven Major League teams he’s called home) in 2008. The Phillies won the series, helped by a 6-inning effort by Moyer in Game 3. Moyer is the oldest player in MLB history to pitch a shutout (47 years, 170 days) and is the only pitcher to blank opponents in games in four different decades (1980s – 2010s).

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George Blanda

No other man played as many NFL seasons as Blanda, who completed 26. Blanda played quarterback and kicker for four different teams during a career that spanned four decades (1940s – 1970s). Only three other players can claim that feat. Blanda still holds the record for most touchdowns in a game (7), was the first player ever to score more than 2,000 points, and is the oldest person to ever start a title game.

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Ted Williams

Perhaps the greatest baseball hitter of All-Time, Williams is the last MLB player ever to bat over .400 on a season, which he did in 1941. His 21-year career in the Major Leagues was twice interrupted so he could serve as a pilot for the U.S. Marine Corps during the Second World War. After his retirement from baseball in 1960, Williams became an avid sport fisherman and was eventually named to the International Game Fish Association (IGFA) Hall of Fame.