Many?
Your story is purely anecdotal and doesn't prove a thing. Statistically there are more older folks in your living area.
The vehicle under discussion here is the motorized scooter. These scooters can be a problem and need a set of safety standards specifically targeted to them. But that being said, acturarially the highest automobile accident rate is among the 16-25 age demographic.
Most older folks that I know are excellent drivers and aggravate the devil out of speeders when they drive the speed limit.
But you are right that testing needs to be more frequent and rigorous. Some will slip through the crack or don't know when to quit. And some are careless to a fault but no more so than with any other group of citizens.
I saw the driver testing folks helping an older driver pass her vision test by letting her'try again'. Another guy had about six pairs of glasses with him and they let him test until he found the right pair. What are the odds he is going to use the right glasses while driving?