It's a stupid rule. There are many variables with people, you can't have a "one size fits all" for heart rate. As Machka said, find your max heart rate by doing. Again, if there are no underlying issues.
It's like the resting hear rate thing. I was reading the chart and it said I should be 55-60 bpm. While I was reading it my hr was 40 bpm.

https://www.castlehillfitness.com/fi...e-220-age-myth

https://www.******.com/r/askscience/...20_minus_your/

https://www.bikeradar.com/advice/fit...a-for-fitness/