I am 63, a bike commuter and road biker. Actually a road triker, as I ride a tadpole trike. 2 wheels or 3 wheels, recumbent or upright, its all cycling to me, and any cycling is good. The original poster had a mention for recumbents, and just in case any new 50+ riders are interested further in recumbents or trikes, here is some introductory info on trikes:
Recumbent trikes are a great way to get some exercise and human powered mobility. Some people get started riding them due to a physical condition, then find that they are so much more comfortable than road or mountain bikes we wish we had started riding them 40 years earlier. I got started due a bulged disk that is now fully recovered. My shoulder keeps me off road bikes due to part of the socket being broken, so I can't lean forward on handlebars of regular bikes.
Trikes are made by several manufacturers, mine is a Catrike, Speed model, which I bought new in 2008. I have not ridden a road bike, nor driven a car to work, since the day I got it, including snow, rain, wind, dust, ice, and wind. And yes, I could drive a car if I wanted to.
Catrike is based in Florida, made in the USA, and their trikes are lighter than most trikes, and have higher end equipment. They are also low to the ground, so are harder to into and out of. That is something you get better at with practice. They are the sports car of trikes: no suspension, light weight, built for speed.
Terratrike is another U.S. manufacturer. They are cheaper than Catrikes ($900 to $2300) , a little bit higher off the ground, and heavier. They have models for people up to 400 pounds (the Rover). The weight limits don't affect riding around town, but if you hit a pothole going 30 mph, the rider's weight can play a big factor in the frame cracking, so for heavier riders they make the frame pretty beefy. For a heavier rider, Terratrike would be a good place to start.
ICE is a super nice trike made in England and imported to the U.S. They are pricey, but super smooth and high quality. They have suspension, which adds weight but some people like it. They are a little higher off the ground than Catrikes, so they are easier to get out of.
Greenspeed is made in Austrailia but are seen in the U.S. from time to time. They are nice trikes, in the same class as ICE trikes.
Hase makes delta trikes, 2 wheels in back, one in front. They are higher off the ground, very fast and very cool. They are at the high end of the scale at about $4000.
HP Velotechnic (HPV) is made in Germany, and is a nice trike for $2000 to $7500. The Scorpion is noted as a great trike by all who own one.
As noted,depending on the rider and depending on the trike, trikes are a bit slower uphill. On the flat they are close to upright bikes in speed. Downhill no bike can keep up with my trike. In rolling hills the downhill speed can be used to build up speed that carries you partway up the next hill. For fun, comfort, and all weather riding, you can't beat trikes. two wheel bents are a whole other story for another time. Bob bicyclepatents.com