Excellent, it's good exercise. Similar to your experience although not as bad, I had experienced swelling in my legs due to vein problems that sent me to the doctor's office. That's behind me now. I recently bought an e-bike, to give me an assist going up hills. The electric motor won't kick in without me pedaling, so I do get exercise, especially at the lowest assist setting. I'm working up a good sweat cycling locally in my neighborhood a few miles at a time going up and down hills. Trying to do it daily. I would recommend an e-bike for most seniors, as it is more strenuous exercise than walking. And more fun.
It's really a nice piece of equipment. I like using the assist at the lowest level because it really extends the life of the battery.
When I can, I don't use assist at all. In traffic you need to, but when I'm just out in a non-heavy traffic area, I can go at my own pace. Then, if at all possible, I simply use it as a bicycle.
With the assist I'm easily up over 20 mph and have had it up around 25 plus.
I've got the four inch tires and I can go off-road. I've had it on the beach at Jalama Beach, up above Santa Barbara. It works good in moist or packed sand, but when it's a fine powder, it sinks in and gets overwhelmed. I road about a mile up the coast at the surf line, and then back and down at least a mile in the other direction. Man, what a kick.
I got it so I could go down to the pacific ocean and ride the bike paths down there.
I realized I needed more exercise, and I'm getting it now.