Heart Rate and excercise

I have a question about my heart rate. Based on optimum heart rate charts,
I should maintain somewhere approx 120-159 hbm. I wiegh 230 and am considered overweight despite a healthy and active lifestyle. Generally, in the warm months, I run 20-30 miles per week and lift weights. During the winter months, I move indoors and run on treadmill and use eliptical trainers. I recently purchased a polar watch that monitor heart rate, and I have noticed that my heart rate generally sticks around the 160-175 bpm range with easy exertion (good easy pace for me is a 9 minute mile)--I am not pushing myself or breathing very hard. I break a sweat usually within the first 10-15 minutes. I hold my heartbeats/minute in this range for anywhere from 30m to 60m depending on my workout. My resting pulse is usually 50-60. Is this typical? I am pushing it too hard (I can't imagine going any slower)? Can I damage my heart? Thanks in advance.

I'm 53 and I did 2*20 minutes of intervals with my HR at 170 earlier today.
This was a hard perceived effort on my account since it is close to my
Lactate treshhold. What I'm trying to say though is that you should forget about those estimated maxHR, even about the estimates of how far off the can be. My maxHR is 190 and according to the charts it should be 167. With you being 20 years younger than me there is nothing strange at all that you do not perceive any exertion at the same HR. Also I've never done a maxHR test.
I just use the highest HR recorded as my max. It might not be my absolute max but so what. It is close enough for me to figure out my HR zones.

I think my heart rate monitor is at fault. When I used the machine grips, my rate decreased to about normal. Any ideas why my polar watch would be so inaccurate?

1) exercise can't harm a healthy heart
2) go by percieved exertion - on your "hard" exercise days your exertion should feel heavy, or very heavy.
3) maximun pulse rate deviates by 15 bpm (standard dev) from formula
220 - age.
4) use your monitor to find out your recovery heart rate. After a minute rest your pulse rate should decline by at least 15 bpm.

http://antwrp.gsfc.nasa.gov/apod/ap031122.html
Lift well, Eat less, Walk fast, Live long.