That formula is complete bollocks, to put it mildly
I'm 56, and when really pushing my HR is around 185, my maximal HR used to be 203, but has dropped with training to 198.
I have a link somewhere to a great article that tells you how to properly work out your heart rate zones, I'll try and find it.
I did used it with my doc, who told me not to worry too much about it, as long as when you stop working hard it returns to normal levels within about 10 to 15 minutes. That's how I cool down now 15 minutes at tapering watts and my HR will fall from the high 180s to 117 to 121