It is alot faster than that, 21 feet can be covered in about 4 seconds by your average person......
Where do these numbers come from? They are ridiculous. Women and old men and some cripples can cover 21 feet in 1.5 seconds. Some take as long as 1.7 seconds. Some young men are faster. I know this because Massad Ayoob gave a bunch of us a stop watch and had us time everyone in the group from start signal to tagging (as in stabbing) a person 21 feet away. He did the same with another bunch of folks at the same time, and they got similar results.
But don't take my word for it - get a few folks and a stopwatch and try it out yourself.
BTW, can you draw and nail a moving target in 1.5 seconds?