If I had any reflexes, I coulda been a fighter pilot...
... or an Astronaut, but my reflexes are total crap!
40/20 means that I can read at 40' what the "average" person can read at 20'. Some people are better thasn average, some worse. it's a bell curve, and as the reflex thing shows, different physical traits are decoupled. The world's great athletes and sportsmen/women are those exceptional individuals who got lucky in several areas at once.
Don't expect them to be brainy as well...