Like you, I was all excited when I started. First with 5 miles! Then 10, now I am doing 20-25 a day! Today is the first day I have taken off in 10 days. Only because I went motorcycle riding and got back too late, but the old legs need a rest day now and then. The most I have done in a single ride is 50 miles. This was at the beach, where the road is flat. I pump a lot of hills around here.
Keep it up, it only gets BETTER!!!