I just started doing the commuting on a bike last week, and am 47 years old and not in good shape. The ride there and back was 18.4 miles, and I was able to do the trip there in 50 minutes @ 9.2 miles. When I got back to my home I was very tired to say the least. Riding here in China might be a tad different than where you might be riding. Just after 5 days of this I am doing ok, and my legs are feeling better and better with each ride. With you being in the best shape of your life, this commute should be a breeze for you.