I took a foil fencing class in college. It required fast reflexes, smooth and coordinated body motions, the ability to plan ahead during the activity, and the ability to instantly drop a plan and capitalize on an opponents mistake or opening. I wasn't very good at it, so never continued after the first class. It required pretty flexible shoulder, elbow, wrist, and hand movements so arthritis might interfere. It was fairly physically demanding, especially the longer matches. I understand saber fencing is more of a workout.
I found road bike racing to be a good physical work out, and the racing events require a lot of thinking and planning, and fast reflexes to exploit a leaders mistake or avoid a wayward rider. Thinking is required in knowing when to make a break, when to draft the pack, knowing the road course and where you do better (climbs, descents, sprints, etc). Even on the same course each event is different, with decisions and mental activity required througout the race. And there are a wide variety of race events such as time trials, individual or team pursuits on the velodrome, hill climbs, etc.
Also, while you can always ride by yourself, fencing alone is tough - your shadow is sooo predictable!
Good luck with the sport!