I'm 66 but have been riding for quite a while. One of the biggest issues is getting a proper setup. There was an earlier post about fitting which is the same thing. Most issues are knee, hip, and back. You don't need a professional fitting, but you should make sure you are not causing any problems.

I have always used the KOPS (knees over pedal spindles) setup or slightly back for mountain bikes. Getting the saddle height correct is also important. The last area is stem length and handlebar height. This is more about comfort and a higher and a bar closer to you may be easier on the back.

As for riding, you should strive to ride with a higher cadence (rpm's) that getting lugged down in a high gear and slowly turning the pedals. Traditionally 90rpm has been the goal, but for recreational riding, I would think somewhere around 70 would be good, maybe a little less. It is something that you can build up and still be comfortable.

John