Welcome back!
I returned to cycling after a layoff of about 20 years, due to having more money, a car, 4 kids and no particular reason I could think of to ride a bike. Then I got rheumatoid arthritis and was told to get exercise. I tried swimming and found it intensely boring and then, in March 2006, I bought a bike. Then, in the September, I bought another. That's the one I'm still riding about and I've done 36000 miles on it.
I did lose a bit of weight in the early years back and I am still a bit lighter than I was 11 years ago, but I have never really managed a lot more than 11mph average. Mostly it's about 9 mph now and I do indeed find that there are not many people prepared to ride at my speed. I've got bags of stamina: completed the Dunwich Dynamo again this month, at a moving average of 8.97mph. I was on my own for about 90 of the 118 miles I did that night.
I know if I had a regular riding companion I would do a lot more miles - when Auntie Helen was still in Essex, she and I would meet most weeks and potter round a 50 to 60 mile route at about 10mph, with tea rooms and pubs for essential refreshments. I was doing about 6000 - 7000 miles a year then. The Dunwich Dynamo is the only >50 mile ride I've done this year.