see your doctor for a referral to a cardiologist so that your heart and oxygen saturation can be carefully monitored while running on a treadmill. this is called a stress test. while it would not be unusual for someone's heart rate to go up this high it would be comforting to know that your heart is capable of handling the load. the fact that you have been active for 18 years is wonderful so i am sure you will pass with flying colors but when you are in your mid-60's it would be good to get the official "okay". i just turned 60 and am now 7 years post emergency bypass surgery. if you are perfectly comfortable playing squash with your heart rate that high not out of breath not breathing hard or panting no chest pain then you simply have fantastic fitness. its a whole body activity utilizing legs and tush as you move about the floor and back and ab muscles as you lean in all directions to move for the ball and start and stop. just be sure you eat a very healthy diet plenty of anti-oxidant rich foods every day and keep a lid on saturated fats in the diet. with a bad diet your heart can develop an alternative capillary network that feeds it as major arteries become blocked from bad diet with good exercise. this does not happen to every one but i have this and i know of a fellow about 60 miles away who does also. he also recently had bypass surgery.
my heart rate often goes as high as 170 beats per minute when i exercise. i am in my mid-60s. should i worry about this? i monitor my blood saturation and it sometimes drops into the low 90s. i have been doing this same kind of workout (squash) for 18 years.