Answer:
Psychomotor speed is the speed at which a person can make a specific response. In general, people slow down as they get older. They take longer to respond, especially when they are responding to ambiguous stimuli. Exercise can be helpful in mediating the effects of cognitive aging.
However, there may be some intentionality of why old people choose to do things slower, unrelated to their declining psychomotor speed. In the context of driving, more factors besides age or medical condition should be considered.
Scientists look at one's Useful Field of View, which is how well someone can extract visual information in a single glance without turning their head or moving their eyes. Performance on this UFOV test predicts driving performance. There is also the AAA Roadside Review, which assesses key functional areas in the effort to get states to have more uniform standards.
Overall, older people might drive more cautiously not because they have bad psychomotor speed but because they are being more intentional and careful with their movements and are in less of a rush.
Hope this helps! :) <3