I just looked, I can't find a ride where my average HR was less than 140 bpm. Most of them are 148-156 bpm. Max is around 170. I'm only 62.
Don't worry about your HR if your doctors say your heart is fine. My heart doctor has told me I can run my heart as fast as I want for as long as I can. And I frequently do. I spend a lot of time at levels that are considered anaerobic. I like the effort, sweat and feeling of having pushed that it leaves me with.
So don't get bogged down with HR numbers unless you are training to correct something specific about how you ride. If you are simply wanting what to me I'd consider a leisurely ride, then that's fine. However don't let your HR number dictate and limit you because you feel it shouldn't go any higher.