Actually, giving the character a bonus to conviction is sort of counter-intuitive to me.
If it's about shoving too much power into something, then increasing power by overcasting seems much more in line with the concept.
If you need a power upgrade to make it playable, buy refinement as power upgrades only and, as has been said, add an aspect denoting his addiction, and maybe another one showing that he is, as you wanted, "young, brash, and solves all of his problems with extreme prejudice....regardless of the cost to his body and mind"
I think there's no need to invent a new mechanic for it.