I maintain a fleet of 20-30 FX1 bikes each year for a youth cycling program. They are a workhorse of a bike and perfectly suited for someone wanting to get into cycling and not have to mess with equipment too much.
As for your riding distance, everyone starts at a different point in life with regard to ability and available time. There is no universal right or wrong way to do things.
If 20 miles of riding has been attained by completing 20 rides, perhaps push yourself beyond 1mi rides. Regardless of how far each ride has been so far, push yourself to go a bit more if you have the time. The good thing about riding on trails is that you can always easily pull off to the side and rest.