This may sound stupid Rocky, and yea, genetics does play a majpr role.

But one thing I have noticed in increasing handspeed, is alot of it is in the mind. I mean, I have worked on tellng myself, 'throw faster. snap faster. Quick man, Throw Quick!" day in and out before ever stepping in the gym, days off, when drifting off to sleep at night. And that shit works.

I'm not discounting various physical methods, am sure as Scrap suggests, there are good and bad ways of going about it. But never underestimate the power of the mind.