The only way to actually determine your true maximum heart rate is a stress test in the doctors office. The way all of the charts calculate max heart rate is only a very loose average. Everyone has a differnt max heart rate and yes with age it generally declines. Can you kill yourself by having your heart rate too high? Only if you have heart problems! Otherwise your body will go anerobic and your muscles will not be able to maintain the work effort that brought your heart rate up and thus your heart will slow down. Men's Health has some interesting reading on the subject. Hitting your max doesn't mean your heart is going to explode, at least not if you have a healthy heart. I am 42 and I just went in for a stress test and my predicted max heart rate was 178. My actual max was 189. Your max can also increase as you get in shape. Glad to hear you are enjoying exersice! Keep up the good work.

dug