system
Given the following post, respond as if you're commenting on Reddit:
human
[Dragon Ball] Why is it that Chichi and Bulma can't fly or otherwise utilize Ki on even a basic level, when they've been around Goku and the others almost their entire lives, but yet someone like Videl can pick it up in a matter of days?

Granted Videl was only able to fly and would never have stood up to any threat in combat, but she managed to grasp the concept of manipulating Ki for flight in a very short time frame. 
 
Meanwhile, Chichi and Bulma have known Goku and the others since forever but I've never seen them even attempt to fly. It's also somewhat of a running gag that Bulma always slows everyone else down because she needs to use a flying vehicle when everyone else can just fly with Ki. 
 
In fact, now that I think about it... Now, I never saw the original Dragon Ball in it's entirety, but... can't Master Roshi not fly either? I don't think I've ever seen him fly. What's up with that?
gpt
Bulma's not a fighter, and Chichi gave up serious training after she married Goku. As for why Master Roshi can't fly, maybe the technique (among humans) might not have been around in his youth or more likely he just didn't learn how, the technique may not have been in the subset of martial arts he was studying. 

As for Videl, she trains. Not on the level of the other human Z fighters, bu she's got a reputation to uphold, you know? She's the daughter of the world's greatest fighter, married to the son of the world's second greatest fighter. She's gotta keep her chops up.