Getting a higher average speed can be easy, but I have some tips for you. First off people who have been riding 30-40-100 miles are in crazy good cardiovascular shape. They have been training for years. The younger you start the better off your averages and mileage will be. Also being an x smoker and depending on how many years you smoked can adversely affect your riding today. But theres hope!

I have found that by watching professional time trialists a good little trick they learn. If you really want to increase your average speed you need to get out of the saddle more often. I have seen that if they hit a small increase in gradiant or they are starting to slow down they get out of the saddle and get back to a higher speed and then try to maintain that higher speed. This has helped me a lot. Just peddling while sitting down won't allow you to get up to a high speed to maintain for longer. Gotta use those calves and glutes more.