I know that athletes have heart rate around 40. Their heart can pump more blood with every beat. That's why it can work with less effort. You say you run with no problem at all so I believe there should be nothing you should be concerned about.
I for instance am a 22 year old male. As soon as I start walking my pulse accelerates to 120 in the first minute, as I get faster it can go up to 180 but I don't run long distances. Instead I walk fast with 140 steps per minute with about 150 HR with no tiredness. And I have resting HR of around 60. My cardiologist was surprised to see such a HR of me on the treadmill and said I am out of condition, I should exercise. D'oh I walk faster than anybody else around, this is just how my heart is.
Sorry I jumped topics a bit but that's so. I don't think you have any problems.

Predicted maximum heart rate for someone your age is around 180bpm (220bpm - your age). You would expect that with the amount of exercise you do in a sitting that your HR would get up there to that. What indicates your level of fitness is your resting HR and how quickly it takes your HR to return to baseline after exercise. If, as you say, this happens quite fast, then that's a good thing!!!