Bill, those are just crude rules-of-thumb.
I was aware of that. The only way to find out for sure what your max rate is to bust your ass, and that takes will power. But at least I was pleased to see that my max was roughly in the normal range for my age. BTW, I've tried to push it to the max on a stationary bicycle and couldn't get it nearly as high, but I've read that is typical. Your max rate will vary depending on the activity.
Re. resting heart rate. A family friend in the US was very healthy but had chronically low resting heart rate (40 like you) & low blood pressure.
In my case, I don't think I had a naturally low rate. The first time that I can recall getting an EKG was in my early 20s when I took a physical to apply to Navy Flight school, and I think my rate was around 72. At that time I was mostly a weight lifter, and never ran farther than forced to by a football coach. But in my mid-30s I started distance running, and my rate steadily dropped. At age 41 I got tibial stress fractures and had to quit running long distances, but I switched to cycling.
Of course at age 74 I just can't tolerate the work load that I used to, so I'm surprised that my rate hasn't increased very much.
I've had several surgeries under a general anesthetic, and I always make a point of warning everyone that they shouldn't think I'm dying on them because my heart rate is low.