The important thing is to keep riding and having fun doing it, how fast is secondary. But if you want to go faster and farther, it takes time and work to increase your speed and endurance. Proper nutrition/fueling is also key. I'm 60 and my max HR is 181. On a fast 25 mile group ride I regularly do it stays in the low 160s for most of the ride. My last ride I averaged 24 mph (flat and aided of course by riding in a pack). I've been riding on-and-off for 40 years but have been training for two years, >8 hrs a week, 100-150 miles/week, 6000+ miles in the last year. When I can't ride outside I do intervals on a trainer or in spin classes. A few books I highly recommend:
The Time Crunched Cyclist. Chris Carmichael (very good general information and explanation with realistic training plans)
Sports Nutrition for the Endurance Athelete. Monique Ryan (excellent nutritional information and specifically how/what/when to eat when training and riding.)
Cyclist Past 50. Joe Friel (a bit pedantic and hard-core IMO, but still mostly excellent info)
These books explain what's needed, why, and specifically how to go about it. Of course the idea is to have fun challenging yourself and improving your performance, not knocking yourself out and taking the fun/joy out of riding. Apply these principles and train only as hard and to the degree that you want to.