Don't ride every day... a few days off is ok.
But also consider a few longer rides. 10 miles? 20 miles? Mixing it up allows you to get stronger. Force your body to adapt to 20 mile rides and the 5 mile rides will feel short.

Make sure your bicycle is well tuned. I could imagine 10 miles dragging a sofa down the street behind my bike A well tuned bike may save that little extra effort.

You mentioned age in the mid 60's. Lots of cyclists older than that. What about weight? Either overweight or underweight can be an issue.

Keep in mind that it may take 10 times as long to build muscles in your 60's as it did when you were a teenager.... and even that wasn't quick. So have a little patience, and keep up the hard work.