[jacobolus]

He also could jump almost a foot and a half higher off the ground than the average NBA player, who in turn can jump almost a foot higher than the average man of the same age.

What proportion of people out there can learn to jump so high, even with extensive training/practice?

[bsanr2]

Hard to know, considering that said extensive training/practice is not as well-known as other basketball-related training, and that the practice of fielding players who would benefit from it is discouraged.

That said, a quick search of "training to dunk 5'6"" on Youtube brings up a number of videos.