The world's fastest man, Usain Bolt of Jamaica at the age of 22, ran a world recording breaking 9.58 second 100 meter dash at the 2009 12th IAAF World Championships in Berlin, Germay. This world record breaking run beat his previous record of 9.69 seconds in the 100 meter dash.
Based on the stats from his 100 meter run at the 2009 World Championships, Bolt ran the entire race - from a standing start - to the finish at an average of speed 23.35 miles per hour. However, Bolt’s fastest 20 Meter split time (from the 60m to the 80m mark) was clocked in at 1.61 seconds. Making Usain Bolt's top speed during the race 27.79 mph.
To put that in prospective, a Cheetah’s top speed is around 70 mph.
Usain Bolt's record by the numbers: http://news.bbc.co.uk/sport2/hi/athletics/8205451.