Welcome, Anasazi!

You are getting healthy benefits from riding. The speed is not the issue, it's the amount of your effort. If you're breathing hard and breaking a sweat, it's doing good stuff. Even if you're just noodling, it's still good.

I think you're asking the wrong question. The issue is not you compared with other 47 YO's, it's you compared to yourself. You're making progress, sounds to me like you're doing okay. Track your time on certain rides, and monitor progress so you can see the improvements. Consistancy is important, getting out 4 o 5 times a week. Sounds like you've got that one covered. To increase your speed, ride fast. And let yourself recuperate. The best way to get results is by interval training... brief exertion and recovery cycles. I'd recommend getting a general cycling book. Greg LeMond's Complete Book of Cycling is a good one for starters. Lots of basic and advanced information presented in a way that is palatable to riders that aren't fanatic (yet ). Remember, progress takes time, you can't rush it but you can delay it.