Those stats come from the National Institute of Health, i.e. the Federal Government. I'm sure they reason they picked those ages is that people are growing up to 20, and after 40, women in particular tend to shrink a bit due to something in the ostroprosis cycle I would guess. So 20-40 is a normal adult range.
I know I'm within a .1 or so of what I was at 20. So at 19 you might grow more, T might help, I don't know, there seems to be no stats on average
And its a mean/median average, which means that exactly one half of all males in the group are taller, one have exactly are shorter than the given number. Why stats is not a mandated course in High School amazes me. So sure, some male are taller, some are shorter. Hell,
* Tom Cruise
(5' 7" / 1.702 m)
* Dustin Hoffman
(5' 6" / 1.676 m)
* Dudley Moore
(5' 2 1/2"/ 1.588 m)
* Al Pacino
(5' 5 1/2"/ 1.664 m)
And if you can act half as well as Dustin or Al, well you will make it.