I think maybe what diminishes our drive to do more is that it gets harder to do more than it used to. Do you have an area of relatively good riding roads where you can do out and backs? When I was starting over in my early 50s, I'd ride away from home until I was tired, then ride back, this long ride just once a week. Another trick is to increase your weekly total mileage by 5%/week. Some say 10%, but that compounding gets away from one too quickly. Getting better at 10%/week is not realistic. This involves a process of planning and then execution. However one does it, that's what one does. In any case, don't just ride around that lake.