Your heart rate while running depends on a number of things. Among others:
- Your resting heart rate (RHR) and maximum heart rate (MHR)
- Your state of hydration, your state of health, how much sleep you get
- How fast you're running, up or down hill, weather, wind, etc.
- The (physical) size of your heart
Your RHR should be taken before you get out of bed in the morning. Do it several days in a row and average the readings. Finding your MHR is more involved. The best way is to have it tested in a lab but that costs $$$. This article suggests several ways you can test it yourself, none easy but doable.
The "220 minus age" formula works for maybe 50% of people. According to one of the study authors, it was never meant to be used for the general population. MHR also apparently depends somewhat on the size of the heart. Smaller hearts pump less per stroke so need to pump more often. (I'll have to try to find the article where I read that.)
150 - 170 may be a good range for you, but you really need to know RHR and MHR to be sure. With continued running, your pulse will be lower at a given pace (and your RHR will be lower). You're probabl better off near 150 for every day runs. On the other hand, as your pulse exceeds about 90% of MHR, you run anaerobically, and your muscles use fuel faster than your bloodstream can provide it. Your muscles will tire and force you to slow or stop. So if you can continue, you're not too close to MHR.
So do a little research and read the articles. You will probably find that 170 is a trifle high, but not a lot. Maybe a good hard run pace. For a not very scientific comparison, my heart rate while running a marathon is about 150 (say, 145 - 155). My RHR is in the upper 40s (46 at the doctor recently), my MHR is 188, and I'm 63 yo.