Pardes,
don't worry about your speed. It's your health and your fun that matter.

I'm 54, and have been biking about 2 years now. Before that I hadn't exercised a day in my life. (except for waitressing off and on). I went from doing 3 mile rides the first year to actually riding 3400 miles last year. Why? because I love riding my bike and I love how good it makes me feel.
My speed has improved slowly. The first year I averaged 9mph. Last year I averaged 10mph. This past couple of weeks I seem to be averaging 11mph.
I figure by the time I'm 85 I'll be averaging 40mph.

I do like to see that I am getting faster- because it tells me I am getting stronger. I don't care so much about speed, I care about the beauty of enjoying my rides. Do what makes you happy and don't worry about everyone else. Good for you getting off the couch!