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
Bitcoin is for everyone. But there will always be something that is hard to understand even for older people. For teens, I guess you just have to introduce it thru a simplest way possible. No need to elaborate it. May be if they know enough basics, that's the time you will explain it further. Explain it by comparing it to more simple things. Time will come, they will completely understand this as bitcoin is blooming in this generation.