Why do height-by-age graphs start at 5, not 0?

Question

As someone who knows nothing about medical science or kids, I have observed that 1-year old male infants often seem quite tall for their age. And I think to my self, “That kid still has ~17 years of growing left, surely the growth rate can’t be linear…”

So I looked up height-for-age graphs to get a sense of what ages have the highest growth rates—when does the fastest growing happen?

• https://www.who.int/tools/growth-reference-data-for-5to19-years/indicators/height-for-age
• https://cdn.who.int/media/docs/default-source/child-growth/growth-reference-5-19-years/height-for-age-(5-19-years)/cht-hfa-boys-z-5-19years.pdf

I noticed the graph starts at age five, not age zero. So that doesn’t help me compare the growth rate from age 0 to 1, compared to growth rates later in life, to get a sense of what age ranges have the fastest growth.

Out of curiosity, why would a graph like that start at age 5?

Answer 1

There are separate graphs for infants, probably to enable a finer scale. Here's an example for birth to age 2:

You can find these easily enough by searching for "infant growth chart".