Welcome Anasazi,
I'm also 47 years and have started cycling again after about 30 years. I ride a Trek hybrid bike.
Here is how I measure my progress: There are roads I have ridden that I never knew existed. Hills that I have climbed that I never thought I would be able to climb. Muscles that ache that I never knew I had. Oh, yes my speed has increased from about 10 mph to around 13 mph.
I never set out to ride faster. I think it just comes from riding more. I started riding because my doctor said I needed more exercise. He recommended 30 minutes three times a week. I enjoy riding so much that I ride at least an hour five times a week. I don't plan on riding competively, so speed is not an issue.
It may sound simplistic but if you want to ride further, ride further. If you want to ride faster, ride faster. If you want to climb higher, climb higher. Just make sure to have fun.
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Wish I didn't know now what I didn't know then. - Bob Seger