There's no specific age to teach them about crypto, well, you just let them know that it exist, then you can tell them how to earn it in the future. I think it's good if he/she is in high school before starting to engage in the community.
12 years and above I think, Just explain him/her the basics, Cryptucurrencies are adults stuffs when it comes to its application. Don't ruin the child's mindset like that. If you want then computer hardware and computer knowledge is essential to a kid, as well as programming. Later when he/she knows this stuffs, they will understand the blockchain even more because they know the theory behind.
Once somebody is able to drive a car, he should be able to understand bitcoin as well and handle it in a responsible way.
The age to get a drivers licens differs from country to country, but as far as I know it's between 15 and 18.
In general I would not teach bitcoin in schools.
Imagine a teenager was tought about crypto currencies at school, opens an account and loses all his money.
I am sure that in case of a lawsuit the school would be held responsible and it would have to make up for the loss.
This is all about individual teachings, how you can make your child view the world in cryptocurreny in a "not all about money" manner. But I think later on this kind of technology will be taught in schools and will be included in the curriculum. This is no different from, ecomomics and finance.