Though Oogway from Kung Fu Panda doesn't get to show off his Badass Grandpa skills much, one flashback shows a fight with fellow badass Tai Lung that lasts all of a couple of seconds. Oogway completely immobilizes Tai Lung with a few nerve taps. Shifu himself is no slouch, trouncing all of the Furious Five at once and holding his own against Tai Lung even though crippled by his regretful feelings.
King Triton from The Little Mermaid. The ruler of the Atlantica Kingdom is an intimidating and powerful merman with a good body build for his age and wields a magical trident as a weapon of choice. He is very prone to anger due to his overprotective personality and his hate on humans. Once he is angry he can be unstoppable, whether he is scolding his rebellious daughter Ariel or facing his treacherous former ally Ursula the sea witch. Hadn't Ariel made an undestructible contract with Ursula, he could have give the sea witch an unforgettable lesson. By the sequel, he became a proper grandpa even though he had already an stablished badassery.
Old Tom from The Mousehole Cat goes out fishing in a terrible storm so his town won't starve.
Zeus from Hercules, the almighty Greek God of the Olympus, who has the power of casting and throw powerful thunders, can animate his statues in his dedicated temples and deal with the omnipotent and extremely towering Titans.
The 2009 animated Pixar film Up has Carl Fredricksen, who's one heck of a badass old guy. Although he technically isn't a grandpa, since he couldn't even have kids. There's also Charles Muntz who was a famous adventurer when Carl was a child, and is still in better shape than him when they meet.
The 2006 animated Blue Yonder film Hoodwinked does this with Granny Puckett, who is a Badass Grandma for Red Puckett. After all, we're talking about a granny who does alpine skiing, skydiving, half-pipe skateboarding, surfboarding, and more, and much like Red, is proficient somewhat in karate.
Rafiki the Mandrill in The Lion King, who can take on a pack of hyenas as well as any lion.
Claude Frollo of Disney's The Hunchback of Notre Dame. Although he mostly makes his soldiers do all the work, he's quite capable of going after anyone himself. He's almost as physically strong as Quasimodo.