Wether elementary, high school, senior or University level, I think crypto can be thought on all levels for a general knowledge.
I don't think crypto or BTC is a proper topic for an elementary school, too early for kids to know about investment and digital currency. Crypto or BTC topic should be a topic for a Senior High School level at least, students have been mature enough in this level. Don't force ourselves to learn it for kids, it only wastes time I guess. For me, the best level to learn crypto/BTC is the university level.