Wow - y'all must be feeding yours right! I substitute-taught at my old junior high a few years back, and I had kids who were not yet five feet tall. In eighth grade.
You must be in Michigan or some such place; here in Texas the only kids under 5 feet tall are fourth-graders or Mexicans.
And as a 6'-4 adult (male) I'm only just above average height among the guys I work with.