Where does the Bible teach an "age of accountability"?

It doesn't.

As to King David's emotional statements made when his child died, we have no reason to think that he had any theological insights. The Bible simply records what he said. Nothing more. Especially when one considers the horrible sin of David surrounding the circumstances of the child's conception, why would we assume that King David had any special wisdom or "inside track with God" on this subject?

Age of accountability teachings arose from people looking for comfort when a child dies. But if we are honest with ourselves, we will admit that the Bible simply doesn't tell us anything clearly on this topic.

Of course, if the "age of accountability" explanations were true, then someone wishing to guarantee the eternal bliss and salvation of a child would simply murder them. That's a disturbing thought. (Indeed, it provides probably the ONLY possible Biblical argument favoring abortion.)

It does not teach an age of accountability though some people might say "12" since that is the age Jesus was in the temple answering questions. It varies with each individual since everyones mind is not the same. A small child knows right from wrong but may not fully understand the consequences of their actions. Same principle.

A prime example of this is found when David's child dies and he stops mourning because he knows he will see him again someday. It is implied that because the child has not reached the age of accountability, he will be with them in paradise. There are more examples, but this is the one most often referred to.

in the teachings of jesus

KJV: Matthew Chapter 13

[13] Therefore speak I to them in parables: because they seeing see not; and hearing they hear not, neither do they understand.

seeing means understanding the world around them yet do not see the things of god

they hear what is said and understand worldly things

yet understand not spiritual things

KJV: Matthew Chapter 13

[15] For this people's heart is waxed gross, and their ears are dull of hearing, and their eyes they have closed; lest at any time they should see with their eyes, and hear with their ears, and should understand with their heart, and should be converted, and I should heal them.

to be saved you have to understand with your mind and heart and see with your eyes means to know and understand what is meant

little children have no such ability to understand nor see

Not sure... I am accountable for my own actions though, I know that much.

I don't believe it does.