if you want to ride farther and longer, go out and ride longer and farther. it's pretty simple. start by setting a goal (I'm gonna ride 20 miles without stopping) and gradually increase that, without worrying about how long it takes you. then switch it up, and start putting some constraints like 30 miles in 2 hours, or whatever.

100 miles/week is a great goal for anyone, and you can easily get into racing shape with a structured plan with this amount of time, but it will likely take you a few season to get there.