Child labor laws were not instituted to protect children like most believe, they were implemented during the great depression along with minimum wage laws and the retirement system as a way to lower the unemployment numbers and free up jobs for others.
If everyone started working when they were young the 20 year old boss wouldn't be a doofus, he would be a seasoned veteran of his trade with over 10 years of experience.
As for marriage, you are correct that a 13 or 14 year old doesn't have a clue about who they should marry... but that was the reason that for all of human history until the last 80 years or so that parents arranged marriages for their children.
I cannot tell you how much we agree on this subject. Repeal of the minimum wage and child labor laws as well as the repeal of all federal mandates on government schools would change the focus of childhood immensely.
That would be "in Western nations" only. There are still many countries where children are expected to work from an early age, and do. I assume there are no child labor laws in China.