Acuity has to do with sharpness and smartness. Do you always get A's in math? Then you have an acuity for numbers.
People often talk about "mental acuity," which is a fancy way of saying intelligence, brains, or smartness. There are specific kinds of acuity, too. As people become very old, they tend to lose their acuity in many areas, including their vision, which is one reason very old people don't drive as well. A 40-year-old quarterback isn't going to have the same acuity for seeing receivers and throwing the ball as a 25-year-old quarterback.