All I can say is holy crap if you can sustain 25+ on human power!
That's not happening for the vast majority of cyclists without electric assist. Any wind at all plays a big role, then add even a small amount of hills, that affects average speed too.
Most riders are between what would be beginners and medium riding experience, and beginners would be lucky to maintain an average speed of 12 mph for 10 to 15 miles.
If someone has a medium level of experience and rides 3 to 4 times a week for 35 to 40 miles each time, they can build up to average 16 to 19 mph, with no wind either against or behind, and negligible amount of hills.
Someone who is very competent, rides on club rides very regularly, and pretty much year round, and goes distances of 50- 60 miles at least a few times a week, can possibly get to 20 to 24 mph average speeds. It's rare. These people are in exceptional shape, with very well defined muscles in their calves, likely rather thin, very aggressively aerodynamic posture while riding,, and probably could easily run on two legs over 8 mph's for quite some distance too.
Averaging 25 mph ? Good luck with that without e-assist, and unless you are in a group where people draft off of each other frequently, or you are not likely maintaining that speed for any meaningful distance. (Over 10 miles ?) Even with no wind , and being on perfectly flat surface, the wind resistance a rider faces at that speed, is exponentially greater than doing 15 mph. Wind resistance curve is not linear, as your speed increases. Wind resistance plays a greater role than any other force.