It would be pretty broken for the person who has it.
In our evolution mankind has had some very nifty things. While there are a lot of animals that can throw or "shoot" things, mankind is the only one that can pick up something off the ground and throw it with decent accuracy at range.
The problem arises in how this is done. To throw something you have to let it go at a specific point that changes based on distance, height and the velocity at which you throw. The timing of this is so precise that by the time you are halfway through a throw, the signals to open your fingers and let it go at the right time is already coursing down your nerves. Individual differences between nerve speed, length and such are relatively minor between people.
Now imagine someone with such absolutely massive differences in their nerve impulse speeds. Their brains wont just adapt, these people will never throw a Ball half as good as anyone else. Instinctively they'll release it halfway the throw, and to learn the complete complexity of throwing a Ball without any support is like teaching current primates to throw like a baseball pitcher.
But the thing is, throwing isnt the only thing that works this way. Most vegetative functions will break down. The act of walking will be harder to learn. Breathing patterns have to be re-learned (I hope your person is born in an era where a machine can breathe for him the first few months) and most importantly... His heart will almost undoubtedly fail.
Your heart has a bunch of nerves over it that deliberately slow down the impulses. The idea is that the first 2 Chambers pump and a moment later the next, causing the neat "thu-thump" of your heart without blood going the wrong way. If these nerves are even slightly sped up ut will cause arithmia's (spelling I know) if not death.
Lets ignore that all for now and look at a person who also has his biological functions and evolutionary stuff sorted out. He acts and breathes normally, can throw and walk normally but he just has very quick nerves and brain processes to give his responses.
He'll seem very witty, (almost) always ready with a response as he'll require less time to come up with one. He'll do tasks like calculations or restructuring much faster, but not smarter than someone with a similar brain pattern. He'll be more accurate than other people as his hand-eye coordination will suffer less from a delay, meaning that anything from throwing darts to doing a high-speed car chase will be easier for him than others, assuming he learns to do it.
Perhaps interesting to think about: sleep patterns. While his body may need +/-7 hours of sleep, his brain would go through the sleep stages much more quickly. He could end up sleeping a lot shorter, but bodily suffer for it as during sleep the body does the most repairs and fighting infections.