What’s an example of something you should wait to introduce to kids?

I wasn’t sure how to word the main question.

You know how people will say kids should do homework every night to get in the habit? They even think elementary age should do it because in high school they will have to.

Or, they should learn about difficult topics like slavery in Elementary, because it’s important to know it in general.

Another example is giving a child responsibility to do something that is difficult at their present age instead of waiting for them to be mentally mature enough.