First, make sure the bike fits. The saddle and bars should be adjusted for a bit more upright and relaxed position than they would for younger people. You should be carrying at least some of your weight on your hands, which will take some of the weight off your backside, this will make longer rides more comfortable. Choose good gloves and good shorts, if you wear cycling shoes, make sure they fit well. Experiment with the adjustments on your bike, it can take some time to reach the best level of comfort.

Use the granny gear, and keep the speeds low or moderate. It takes time for the muscles, tendons, and ligaments to adjust and build up. As a younger racer, I would work up slowly after the off season, and would not begin training at 100% until after 6 or 8 weeks of more moderate riding. As I am not young any more, it takes a couple more weeks than it used to. Once your body is more used to cycling, you can begin to push bigger gears, and pick up the pace.

Stretching is important. Many people, for whatever reason, scoff at stretching before and after a ride. But it is a great help, it helps you warm up more quickly during your ride, and helps speed up your recovery after your ride. There are lots of videos on YouTube which show good stretching routines for cyclists.

Have fun on your rides. Enjoy the scenery, the fresh air, and try to go to interesting places. As a method of fitness, like any other, cycling needs to be done regularly. What I like about cycling is that it allows me to maintain my fitness while allowing me to go to more distant and interesting places. And riding a bike relaxes me, and releases stress. I don't listen to music while riding, and I try to keep my head empty. My mind is kept busy during the day, and at night I am often dreaming. Cycling is a good chance to meditate, I focus on my pedaling and breathing, pedaling in circles and pacing myself. Being able to ride regularly makes my life better.