Not just the old
There are people of all ages who shouldn't be driving.
- Those with physical infirmities such as poor eyesight
- Those with social or mental problems such as fondness for booze
- Those of a nervous disposition who might get distracted by, for example, a wasp buzzing around their head
- The impatient
- The easily-distracted (especially in the presence of distractions such as friends or children).
- The absent-minded or dawdler
- The over-confident/complacent
Perhaps it would be simpler to summarise, and just say "normal people" as a first-order approximation.