The reaction test on a computer is directly linked to your ability to click a button.
As long as you are conditioned to that reaction, you should be in the 200ms region. If you aren't, you will be slower. Everyone's reaction times are similar, just not everyone is conditioned to react fast, when they can.
All I'm saying is you can practice reaction tests. It doesn't make you faster in general.
You get faster at doing something by doing something.