Can I get ready for a Century without riding 100 miles per week?
If you’re only able to do long rides on weekends, than you’ll have to make up for the lack of mileage in other ways. For example, get a stationary trainer for your bike and put in several hours of indoor riding each week. Get out once or twice a week, and do hill climbing or speed work during these shorter workouts. Save your longer rides for the weekend when you have more time.