I got freaked out a few years ago because once I started monitoring my heart rate (via a HRM strap first, then via my smartwatch) I started to realize that my heart rate was NOWHERE near the "220-age" guideline...
I was hiking with buddies and remarked my HR was 179, and they looked at me like "how are you still upright and alive?!?!" I was huffing and puffing a bit (we were halfway through a 3000 ft vertical climb), but I was fine.
Couple that with some arrhythmia in my family history, and I was worried. This was right around the time I'd gotten divorced and met my wonderful [now] wife, so I was maybe not interested in my heart exploding if I kept up the strenuous hiking.
So I went to a cardiologist, got a 24-hr holter monitor, followed by a stress test. Did the stress test and he tells me "you did much better than most of my patients", which should sound great but most of his patients are geriatrics with heart problems!
Long story short, apparently my peak heart rate is somewhere in the 203 range, where "normal" for my age would be around 178.
Yet another area of life where I'm way out on the long tail of the distribution.