First of all understand that the rate of improvement is proportional, so if 25km is long to you adding 20% is only another 5km. OTOH as you become stronger the rate of improvement will increase, and thing will happen faster.

There's also the hill factor. People in hilly areas have to work much harder than those in the flats to cover the same distances. If the hills are steep, one mile of climbing may be more taxing than 10 or 20 miles at a comfortable pace in the flats. In my experience, hills are the biggest cause of discouragement for cycling because there's nothing you can do about them. However, you'll find that with time, the hills get flatter and shorter (seemingly), and you'll have the advantage of being to climb when necessary whoch removes the biggest barrier to longer rides.

Finally, do not ever compare yourself to other riders. That's an exercise in futility. All that matters is that you're getting stronger and the ratio of enjoyment to effort is tipping in your favor. As you gain the power to climb hills, and ride the distances that you choose or time allows, you'll be riding without worry and your bike will take you wherever you want to go.