Am an advocate of biking, as an alternative to walking, as I believe it puts less stress on the knees and hips, and calls for the same kind of muscle stretching as swimming, without the shock of continuous impact. (just my opinion)
Counting the years, now more than 75 years of riding bikes. My 1992 "Offroad" Mountain bike, the 1980 Motobecane, and the 1974 Schwinn Bent Tube Sprint still serve me well. Also a more modern 1997 Mongoose mountain bike, that gets the most use.
No longer do the 35 mile treks, but have moved back to biking 2 to 10 miles a day when there isn't any wind.
I stay off the traveled roads. Lots of roads and trails at Woodhaven, but in our CCRC area, limit the riding to the side streets. Don't know if it's just my imagination, but it seems that many car drivers on the higher speed roads don't give bikers the room required by law. That's ok for the bikers who are young, strong, and can hold a straight line, but not so good for us oldsters.
As to toys... yeah... guilty. All together, here in Peru, Florida and Woodhaven Lakes, 8 bikes... all in perfect, well tuned condition. In the first 15 years of retirement, bicycle repair and tune up was one of my volunteer contributions to our retirement communities.
All in all, biking seems to be the easiest way of putting off the inevitable aging of the body. For those who haven't been riding for a long time, I usually recommend taking it slow for the first few days or weeks. As pointed out in other posts, correct seat and handlebar height is extremely important. Watching older people rediscovering the sport, the biggest problem is that they set the seat too low, stressing the knee muscles and joints. That's okay in the early days, while learning balance, brakes, and speeds but unless the seat is reset to the correct height, newbies often find biking to be too hard on the body. The other major problem comes from not keeping the tires at the correct pressure... makes for much more work.
No new bikes for this old bear... I like knowing the history of the older bikes... Schwinn only built a few hundred of the "bent tube" bikes, great story behind the scenes. Same interest with the "Offroad" a bike that was 10 years ahead of its time, with some features that even now are still being discovered. It was the precursor of Trek... Who here, ever heard of an oval crank, with sharpened teeth, or a drive chain without a master link? a front elastomer suspension, and and single pivot rear suspension.
Many bicycle history websites that track the technology from the early 1800's, through the high wheel "boneshaker" in the 1870's through to today's high tech carbon framed lightweights.