I'm 54 and about 180 lbs I can tell you I had the same experience when I tried running with the heart monitor for the first time. My max is about 180 bpm and I hit that while running with what I considered a good but not max effort. At 180 bpm on a bike I am about done.

It turns out that because you are supporting your own weight while running your heart rate typically will be higher for a perceived effort