The perception of what is considered "fast" for a human can vary depending on the context and individual perspective. In terms of running speed, 20.5 mph (miles per hour) is quite fast for a human.
To provide some context, the average human running speed is around 8-12 mph, with elite athletes reaching speeds of 15-20 mph. So, 20.5 mph would be considered faster than the average person and even faster than many recreational runners. It would generally be considered a fast running speed.
However, it's worth noting that the concept of "fast" can differ based on various factors such as the distance covered, the duration of the effort, and the specific sport or activity being performed. For example, in the context of sprinting or short-distance running, speeds above 20 mph are more common among elite athletes.