Hey there K, you have this goal of 25 miles (approx 40kms I think)

But what kind of speeds have you been riding? What kind of terrain would your 25 miles be over? More details would be useful please.

For me a goal of 16kph would have been too slow on a flattish course when I first started. But it would have been a good challenge on a course with rolling to mild hills.

Great that they encourage goals, and that you are thinking about realistic ones. My biggest problem in my first year of riding was getting way toooo enthusiatic with my goals and then being disappointed.