It's possible that you could live longer, but not forever. My dad's in his late fifties, but he doesn't look a day over forty. I do use some when I fly, but ki's something that gets replenished with food and rest.

[It's that last inquiry that gets her thinking.]

There were these little devices called scouters that would give a reading on what someone's power level was at. They're not really in use anymore, though, since they weren't produced on Earth and they break if someone's power is over a certain level. Trained fighters can sense approximately how powerful someone is. That's...surprisingly hard, though. Learning to fly was way easier.