The 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 difficult. Best to wait until the person reaches late teens and then explain
Explaining Bitcoin is really hard especially to older ones including myself of course at first I really do not understand how bitcoin works and how to start it. I even took many months to decide if I start or not since that I can not really understand it. But explaining it to children or teenager maybe it is much easier since the era of bitcoin is millennial era. it's all about technology digital world which bitcoin is made off. Teenagers nowadays are much more knowledgeable when it comes to digitals internet etc. Just explain to them the very major thing of bitcoin and they will automatically study everything.that is for sure.especially money is involved in it.