Damage fills it up. If Vegeta wrecked SSJ2 Gohan in 2 seconds (think Android 17 vs Trunks), he'd fill it up just as fast. This could, conceivably, also happen to a SSJ Goku that's stronger than SSJ2 Gohan.
Vegeta is (probably) talking about when they're in the same form when he says "Our powers...
Yeah, not super commonly, but commonly enough for it to be notable. What do you mean "How does that work?"? It just does.
HxH, FMA, Hellsing, Shaman King, Fruits Basket, and Evangelion are some examples of anime that have been rebooted.
Ki reserves = 10,000
Stamina = 100%
Full power = 1000
Goku uses a casual KHH
KHH = 3000
Stamina remains unchanged
Ki reserves = 7000 (or a bit less)
Stamina = 100%
Full power = 1000
Goku fights and then uses a full power KHH
KHH = 5000
He gets tired
Ki reserves = 2000 (or less)
Stamina...
The different time period or whatever doesn't mean anything, sekuhara jokes are not exclusive to any time period (or culture for that matter).
I thought the Roshi jokes were fine; a bit repetitive after a certain point, though there's a lot worse out there in that regard (see above)
There were no such talks about Gohan being in a different league than Goku after his powerup either (I'll argue that he is in fact in a different league below). He is called amazing and such, and at a couple of points called something like "the mightiest of warriors," but no direct comparison to...