The boys...compared

I was looking at the boys growth charts and found the most intersting thing...

At 15 months Ethan was 21lbs 6oz and 31" tall with an 18.5" head
At 15 months Ryan was 21lbs 10.5oz and 31" tall with an 18.25" head

Practially identical - the small difference could simply be explained by different measuring equipment, human margin or error, or especially timing within the 15th month.

WOW!

Additionally, Ethan was considered 15% in weight while Ryan, only a few ounces heavier was 20% and for height they are both spot on average at 50% and ditto for head size.

I used an online height calculator...and got this back for Ethan (it starts at age 2 so I can't calculate for Ryan yet):
Your son will likely be 6 feet, 2 inches tall at age 18.This prediction is a "best guess" but it's still just that -- a guess. Based on the formula we used,* there's a 58 percent chance your son's full-grown height will be within 1 inch (above or below) of this prediction, an 85 percent chance it will be within 2 inches, and an 96 percent chance it will be within 3 inches.