Any athlete over the age of 45 has the tendency to be a badass grampa by the standards of the sport, as their performance starts to wane as they get older.
Pitcher Nolan Ryan threw fastballs in the 90-mph's and two no-hitters over the age of 40.
And in his final season, when he was 46, he hit Robin Ventura with a pitch. Ventura charged the mound to fight him, and Ryan kicked his butt. The real kicker: Ventura was ejected from the game and Ryan wasn't.
George Foreman. Won a heavyweight boxing championship aged 45, and STILL can beat the crap out of anyone.
Evander Holyfield is trying to follow his footsteps, at the age of 48.
We must mention boxing's original Badass Grandpa Archie Moore, who won his first world title at the age of 39 and defended it for the next 10 years. His second to last fight was against a young Muhammad Ali well into his 50s, after having begun his career when Joe Louis hadn't even won the title yet. He still has the all-time record for most knockouts, 131. Think about that. The man had more knockouts in his career than Oscar de la Hoya and Floyd Mayweather have fights combined.
Bernard Hopkins became the oldest man to win a world title at 46 by defeating a man nearly half his age and who was considered the top light heavyweight in the world. And it's not like it's a one time thing, Master Hopkins has been outfighting younger men for the better part of the last 12 years. The only men who can claim wins are Jermain Taylor (and both fights were controversially scored, most people thought Master Hopkins won), and Joe Calzaghe (a decisive win for Calzaghe, who himself was a cagey, grizzled veteran at 38). Master Hopkins eats, sleeps, and breathes boxing and says he'll keep fighting at a high caliber until he's 50.
While not as old as some on this list, Brett Favre was literally a grandpa during his final years with the Minnesota Vikings, and was still one of the most feared players in the NFL.
George Blanda started his NFL career in 1949. He ended it in 1976. He only missed one season in that span - 1959; and then only because Chicago Bears owner/coach George Halas wouldn't let him play quarterback anymore (In 1960, he signed with the Houston Oilers of the fledgling American Football League). He made All-Pro as a kicker in 1970 and 1973 with the Oakland Raiders.
In 1970, after Blanda's last-second field goal against the Kansas City Chiefs salvaged a tie, Chiefs owner Lamar Hunt famously quipped, "Why, this George Blanda is as good as his father, who used to play for Houston."
In August 15 2009, Fred Ettish, a 53 years old karate instructor, scored victory in CFX-Gladiator Evolution against Kyle Fletcher, who was almost 30 years younger than him.
Any tenth-degree black belt. Since almost every martial art requires at least half a century of study before you can try for tenth-degree, these are some of the most dangerous old men/women alive. (Apparently, martial arts is second only to swimming for exercise, as proper training will work every muscle group.)
Keiko Fukuda just advanced to tenth degree black belt in Judo. Age? 98.
One of the original founders of SCA, Sir Paul of Bellatrix, who participated in the crown tournament 2011 in the age of 73. He still teaches SCA heavy combat.
British ex Formula One driver Sterling Moss has stated he's glad he was racing in the era he did because it's too safe now for his tastes.
Not to mention that he didn't retire from motorsport in general until 2011...when he was 81.
Former Indy Car, Formula One, and NASCAR driver Mario Andretti, now in his 70s, still drives race cars, including the two-seater car at all Indy Car events. Son Michael is a team owner (and former driver) in the series, whose drivers include Marco Andretti, Mario's grandson.
In NASCAR alone, Mark Martin counts as he is 55, is in a part-time ride with the successful Michael Waltrip Racing, and despite his part-time schedule in 2012 was able to win multiple poles and a number of top-five and top-ten finishes, including a runner up finish in June at Pocono to Joey Logano. Martin probably fit more aspects of the trope in 2009 when he was driving full-time in the #5 Chevrolet at Hendrick Motorsports: five wins, seven pole positions, 14 top-five and 21 top-ten finishes, and a runner-up finish to Jimmie Johnson.
Ciriaco "Cacoy" Cañete, one of the grandmasters of the Doce Pares School of Eskrima and developer of Eskrido (Eskrima, Aikido, judo combination). Born in 1919, he is still quite capable of kicking ass. Go to youtube and search for "Cacoy Cañete" and you'll find many videos of him in a demostration almost nonchalantly disarming and/or knocking down his students or fellow eskrimadors. Some of those guys have been doing Eskrima for years, even decades, and he still knocks them down without even moving from his spot.
He's also had experience as a guerilla against the Japanese during World War II.
Leroy "Satchel" Paige, the oldest baseball player in history, with a 40 year career that he only ended at age 59. In 2010 he was named the hardest thrower in baseball history, having garnered praise from the likes of Joe DiMaggio, Bob Feller, Hack Wilson, and Dizzy Dean.
Jeannie Longo-Ciprelli, a French racing cyclist, born 1958. Won her first french championship title in 1979 - she started riding a few months earlier. Has since won 57 more titles (including some world and olympic medals), the last one being in 2011. Today, her rivals are 20 or 30 years younger than her. And she still beats'em.
Morihei Ueshiba, founder of the martial art Aikido. Even at an advanced age, five grown men in their prime were unable to take him off his feet.
Aladar Gerevich, a member of the Hungarian sabre team, is the only Olympian to win gold in the same event six times. In 1960, he earned his spot by challenging each of the other members to prove that he was still fit at the age of 50. He led the team to gold as its captain.
Tom Coughlin still coaches the New York Giants as of the 2013 season at age 67, and has no plans of retiring any time soon.
Steve Spurrier, currently at South Carolina, will be 69 during the 2014 season.
Bill Snyder, now in his second stint at Kansas State, will turn 75 during the 2014 season.
John Gagliardi, who won more games than any other coach in college history (mostly in the small-college NCAA Division III ranks), retired at the end of the 2012 season at age 86. (He had been coach at his second and final school, St. John's of Minnesota, for 60 seasons.)
Amos Alonzo Stagg, one of the pioneers of the sport, was a head coach until he was 84. He then moved to another school and shared head coaching duties with his son for six more seasons. After that, he was kicking coach at yet another school until finally hanging up his cleats at 96. And he lived for another six years.
John Henry was U.S. Horse of the Year in 1984 at age 9—an advanced age for a competitive racehorse, and certainly old enough that he could have been a grandpa if he hadn't been gelded.
English steeplechase racer Red Rum (also a gelding) won the Grand National, the world's most prestigious race of its type, an unprecedented three times—the last in 1977 at age 12.
Born in 1950, Tom Watson remains one of the most important active players in golf, and not just because he can still kick butt among his fellow seniors. He was one bad break from winning the Open Championship at age 59, elected for his second stint as United States Ryder Cup captain for the 2014 event (more than two decades after his first), and is still plenty capable of making cuts at major championships and the occasional down-the-road PGA Tour event.