I'm 26 and haven't ridden a bike since I was 15. I decided to start again and purchased a nakamura crossland, last Saturday, to get back into action. Last Sunday, I did 17km in 50 minutes on a mostly flat road. I didn't want to start too hard, afraid to hurt my legs. In the end the only thing that hurt was my butt, I probably need a better saddle. I was wondering what distance and speed I should aim for as a beginner, in order to improve my stamina.
P.S. I decided to purchase a bike to lose weight and enjoy the countryside. Maybe it's relevant for choosing the right distance.