Kick Buttowski/WMG

Wade has been seriously abused and/or neglected his entire life.
He's made subtle complaints about his stepmom a time or two, and the episode "Live in Wade," he  and explicitly states that he has never slept in a bed before, and that he has night terrors, which are commonly caused by abusive situations.

Kick has some sort of terminal illness
His love of stunts has gotten to such an extreme because either he wants to get the most out of life and figures he'll be dying prematurely anyway, or he would rather die a cool death than be overtaken by some lame illness.

Kick is "extreme" because he is overcompensating for something.
He has already been insecure about his height. What if this applies to his other body parts too? Or, he could simply be an Armored Closet Gay.
 * What about the one where he fell for that daredevil, stunt double female.
 * Isn't he too young to worry about that or care?
 * Given how low his voice is, his worries very well could be just the opposite.

Kick is purposefully speaking lower than his voice actually is.
Some of his 'oof's sound way higher than they should.

Kick isn't human.
He was made by the government to be able to do more, and survive more, for whatever reason. He was locked away in Mellowbrook ala Truman Show Plot to be subtly made into an awesome dude with awesome skills, as it is the perfect place for all fear to be lost. His desire to become a daredevil was unexpected but not unwelcome.