First of all, to clarify what reaction time is and how do we understand - it is a length of time measured between a stimulus and your response to that stimulus controlled by your central nervous system - usually it is a fraction of seconds between 150 and 300 milliseconds.
Based on our users’ data, of over 500 thousand players, we can clearly notice a significant decrease in average reaction time and rise of steam ranks or Faceit ELO scores. Many results may cause this result. One of them is of course used devices, especially your monitor, keyboard, and mouse. Professional CSGO players and higher ranked players always play on at least 120Hz refresh rate displays that give them lower video latency and increase smoothness while moving your mouse but also use best-in-class accessories that minimize their input lag. Other important factors are our genetic preferences and fatigue, it's a no-brainer that we shouldn't force ourselves to play without any breaks or every night until late hours when our body and mind should have a rest.
In terms of genetics, it is proved that the older we are the slower our reaction is, but also some of us has simply better predisposition to act faster than others and you cannot reach any level you want despite how hard you train but don't worry Counter-Strike is not only about reflex and reaction time, it's just one of many aspects you can gain advantage on, but there are much more which can make you a great player.
For pro players, we've taken just players from the top 20 teams and their average reaction time from the last 10 maps. What can be observed is that the slowest players are those who mostly play with an AWP. Our hypothesis is caused by common long patient scoping and precise aiming to make quick shots right after noticing the opponent on the screen. While shooting/tapping with AK-47 you know you can use 30 bullets so you can use bullets one after another controlling spray at the same time, but as an AWPer, there is very often only one chance after which one you need to reload your weapon and this may be crucial to use that time for the opponent and gain space advantage during the round, so sometimes it's better to slow down a bit and shoot the target rather than shoot as fast as you can and miss it.
Considering how important reflexes are for Counter Strike players - introducing exercises and tasks to improve this element is one of our top priorities, so you will soon find integrated training sessions focusing on reaction time on GGPredict.
Kuben gave us a great way of training your reaction time offline with a friend:
We train with tennis balls - 1 person holds two balls in both hands, and the second person holds his/her hands on the clenched hands of the first person. The person holding the ball at any time opens his hand and lets go of the ball. The second person tries to catch the ball falling down. This is a great exercise to warm up before a match.