Best way of explaining is using the gold analogy.
But I think explaining it to a person in his/her early teens will be quite diffiicult. Best to wait till the person reaches late teens and then explain
You have a point, if a person is willing to understand what bitcoin really is, then it is so easy for them to understand.
Willingness is one way to understand quickly. If we teach someone what bitcoin really is, we need u to teach them one step at a time inorder for them not to scramble their minds.