[Jacksonlll]

If that starter was using four times the power, it would be glowing red hot. It only takes so much power to spin an engine. You can't make it use four times the power. The power used remains about the same, so at twice the voltage, the current draw is about half. That's why the world uses 20,000 volts when they transfer power over the high lines. So the current would be small and carried by small, light wires.
If you were operating a heating element, then 12 volts would let it use more power and glow like a light bulb. The starter motor puts out just so much power.
I'm done with this.