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
I think you're actually right, I have a cousin and he started to earn bitcoins since the last month of 2015 he was 10th grade student at that time and after a month of doing faucets and captcha works he started to invest but unfortunately he was scammed by a hyip sites so I decided to teach him how to properly invest and I also introduced him to trading. I think it depends on a teenager if he or she was very literate on using different devices especially computers.