I really like the US take on this one actually. I'm pro ebike and absolutely love motorcycles, but 45 mph is too fast to not require a licence.
Here we have 3 classes numbered as such. Class 1 is 15 mph pedal assisted, class two is 20 mph pedal assisted, and class 3 is 28 mph and allows a dedicated throttle. Class 3 often has limitations for certain bike trails, but most class 3 comes have variable modes to limit them to class 1 and 2 speeds. Generally as long as you're following trail speed limits you really don't have to worry.
This part varies by state, but in general anything over 28 mph is considered a moped and requires a proper license. As an avid motorcycle rider I feel even 28 might be too fast for non-license, but I also understand keeping up with cars, especially in cities, is way safer so I get why the limit is a bit higher than you'd expect.
Ohio State actually allowed desire paths to form and then paved over them later to make sure the paths were efficient and would be properly utilized.