Solid Snake (“Old Snake”)
Series: Metal Gear Solid
Let's just go ahead and get this out of the way now. When anyone thinks “badass old guys” and “video games,” Snake should come to mind. Although if you really pay attention to Hideo Kojima's absurdly convoluted story lines, you'd know that a cloning error accelerated his aging process.
Series: Virtua Fighter
Do you remember this guy from Virtua Fighter? He was actually a pretty awesome character to play. A 97 year old martial arts master who also happened to be a raging alcoholic. If memory serves correctly, several of his special moves involved drinking from his trusty urn-bottle thing.
Series: Teenage Mutant Ninja Turtles
“Let me get this straight, you're an incredibly old guy who, long ago, was transformed into a human-sized rat, and now you live in a sewer and train human-sized turtles to fight against never ending hordes of ninjas. I see.”
Sure, Splinter isn't technically an old “dude,” but there's no denying that he's badass. He might act like a decrepit old rat, but throughout the lifetime of the series there's been more than one occasion where he whooped a little Foot Clan ass with that staff of his. That's no old man cane.
Series: Star Wars, duh
Who else do you know that's 900 years old, a foot and a half tall, and can schwing a lightsaber with the best of them?
The Old Man From Zelda
If you remember this guy, you know that he lived in a cave and sold young adventurers things like bombs, weapons, and some kind of meat on a stick. Sounds pretty badass to me.