When you get older it takes longer for the body to recover. You mention you are in the best shape of your life, but what does that mean? The best cycling shape. The best cardiovascular shape. The best muscular shape, etc. You use different muscles cycling than you do if you just go to the gym. How exactly are you taxing yourself Do you do HIIT, Linear Periodization, Non-Linear Periodization or something else?

I'm not trying to dissuade you in anyway. I consider myself in good shape, but i'm not ready to run a marathon. My commute is only 3 miles each way and i've been doing it for about 2 years. I'm not sure if i am ready to tackle a 20 mile roundtrip coummute however. Go out and ride the route a few times to see how you feel. If no problems than good luck and continue commuting.