Lots of misinformation about max heart rates. Remember the old formula:220 minus your age. Found to be quite invalid. Measuring max hr with a heart rate monitor (Garmen/Polar, etc.) gets it pretty close. Under strict lab conditions with calibrated equipment monitored by competent exercise physiologists is probably the "purest" way to figure out one's max. Several tests over a period of a few weeks under the same environmental conditions produces the closest thing to your real hr max. Even then, there can be quirks.
Most literature agrees that we usually loose some of our hr max as we age. When folks see a rise over the yrs more than likely they never had an accurate max hr reading. My max hr was 207--attained at the end of numerous hot, gruelling finish sprints in running road races. Over the decades of my running I have seen it gradually drop. Currently at age 66-my max was 198--about 6 months ago. I find after competing in over 450 road races I may not want to put out quite the effort I use to as in my 30's, 40's and 50's. Also, most folks measure 10%+ difference in max hr between running and biking, with running being usually the higher. Hey, I am glad I can still have a heart rate I can measure. Nick