Keep in mind that my only basis of comparison is myself and my wife who is 3 years younger than me. Her numbers seem to be inline with mine for max heart rate. I also know that max heart rates vary from person to person, but I am far from an expert. Using myself as an example, I road 20 miles recently both ways and exerted myself pretty hard the entire time. My max heart rate was 185 and my average was 164. The other day I ran 5k (I rarely run), and I wanted to beat my best time, and my max was 193 with an average of 169 which is probably pretty close to peak output for me. BTW, I am 38, with a similar build.

I hope my comments aren't taken in a negative way. I am not trying to directly compare or anything like that, or diminish how happy you should be. I have been riding all my life, but only started riding regularly again this year. In some ways there seemed to be some similarities between us, and I thought I would share my experience. In fact I started out the year around the same 13.7 average speed, and it seems that our current average speed is pretty close. The 20 mile ride I mentioned earlier was with an average speed of 17.1mph. I guess part of me wonders if you would have been closer to 17mph also if you got your heart rate up a little higher which I suppose is the primary reason why I posted in the first place.

Oh yeah, in regard to finding your max heart rate, there are some calculations you can do to figure out your max, but those generalize a lot and are said to be inaccurate. The best way is to be tested by a professional. I figure that 193 is probably pretty close to mine. I have never gone higher than that intentionally or unintentionally, and I would probably puke or black out if I went much higher.

Anyhow, congrats again on a very nice personal best, and good luck on your quest to get faster.