I know what you mean...

...my 9 Yr. Old is going on 19!  While he may not be wearing a size 9 shoe yet, he is close.  However, if it's chemicals they're putting in the food, then they've been at it for awhile.  I wore a size 9 when I was 9.  I have an older brother who's 18 years older than me.  By the time I was in 3rd grade (age 9) I was taller than him (5'9") and wore a larger shoe.  Ironically, and rather fortunately, I stopped growing at age 15.  So I'm only 6'1" with a size 12 shoe.  People often wondered and commented that I must've been on some kind of chemical diet when I was a little kid, and then stopped when I got to my middle teens, LOL.  My 9 year old is bigger than I was (except for his feet) at that age, and my 2 year old son is even bigger for his age than his older brother was.  Everyone speculates that my boys will be very tall due to their size and the size of their parents (my wife is just under 6'), and perhaps they will.  But my father is 6'4" and everyone thought that I'd be huge based on that & my size as a little kid.  So, we'll just have to wait and see.  BTW, 40-YOV is an hilarious movie, and I think you're wise to only show him the scene you referred to.