In Scotland, elementary school is called primary school and students start out at primary 1 which they are 4 and 5 years old.
Interesting, I think I was 5 when I started 1st grade, I could be wrong thoug
I believe I turned 6 right when it started. The UN had a goal of making sure there was universal primary education by 2015. So that means that every child everywhere completes this first bit of education.
I distinctly remember being a year younger than all my classmates throughout gradeschool. I recently heard the US is withdrawing form the UN is this true?
If this is true, it could be detrimental to human rights. These are essential for children to hit developmental goals.
It would be very sad, that is why some countries have smaller people on average than others - malnourishment
That's correct and there is so much more than only physical development but psychological and emotional are important to. This also lets children grow from being dependent on another human being to becoming autonomous. 
Yeah love and nutrients are probably the two most important factors to child growth, that and socialization
Very true and if these stages, if you want to call them that, aren't met then the markers they hit at a later age are affected. It's like a domino effect.