Best thing I ever did fitness-wise was to take up biking. I used to be an avid and competitive runner (60 miles/wk., with a training pace of 6:30-7:00/mi.). Biking is great because it’s low impact - easy on the joints!
At 58 years old, my resting heart rate is 42, BP is 110/60, and weight is only about 8-10 lbs more than high-school. I rode just over 3,000 miles in 2016, and usually will average between 18-19 MPG for my regular rides of 40-50 miles. Did a few shorter rides (25-30 miles) this summer at over 20 MPH average.
I highly recommend it to anyone! Start at your local bike-shop and get a decent entry-level bike. Find out about local group rides, and go with them as often as you can - you’ll be safer, learn more quickly, and have a support mechanism there among the other enthusiasts. If you like travel, there are organized events/rides - usually for charitable causes- and often in really nice places that are themselves worth the trip.
Seeing this Frenchman still going at 105 is inspirational! Gives me something to shoot for.
Biking is a great exercise and as you noted, a low impact one.