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".
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.