Motorcycle & Scooter

... is a head injury, even a minor one. That's how my dad died: subdural hematoma from a minor fall at home.

I would suggest a small road bike on back roads -- cruise and enjoy the scenery with little or no traffic. In my experience with both dirt and road bikes, spills are more common in the dirt. All things being equal, dirt spills are less damaging to the body, but in your case all things are NOT equal: a minor spill for you would be a major problem.