My first ride on a "real" bike, more than 40 years ago, was 12 miles, and I felt like I'd ridden to the moon. Last year at age 66 I did many 50+ mile rides and didn't feel like I was doing enough, but I've been retired for a couple of years and put in a lot of miles.
Do what you can do, and don't worry about other people's rides. As a rule, you'll have fewer injuries and burn out less often if you take a day or two off each week and don't add more than about 10 percent to your weekly mileage each week, but it would be pointless for anyone to tell you how far to ride without knowing anything about you.