When I started riding, on a mountain bike with slicks, I didn't have a computer. After about 6 months, I got one. I seemed to be averaging around 12 mph. After I got my first road bike, (another year), I was able to get my average up to around 13.5-14. Then I got a carbon road bike. By this time, I was fairly obsessed, after 3 years. My average sat around 16 for a couple of years until burnout, illness, and injury brought it down. I still look at my average, but I no longer obsess on it. My goal is to enjoy myself. Basically, I ride in a hilly area, and on those rides my average is anywhere between 13.5 and 14.5. On flatter rides, it's closer to 15.5-16. I do have a computer on my commuter bike, but I never look at the average, just the total miles I have gone. It's a heavy steel bike, usually with a loaded pannier. I enjoy just cruising a long on that bike.
I feel stronger this year, and perhaps my average will go up. But, my goal is to not burned out/tired by the middle of the summer, which often happens. So, I am starting slowly.