I feel that old people generally don't like to be taught. And so I think the word 'teaching' is not the proper term to be used for them. I guess it's more appropriate if one does it in a manner of somewhat like sharing stories about bitcoin. Old people like to hear stories of all sorts. It somehow gives them the ability to use their imagination and develop their critical thinking. By a story-telling approach, I believe the old ones are more inclined to listening especially when once in a while you insert it with some nice jokes. They like to smile, to laugh and to be merry. It takes time though for them to understand much about bitcoin but, for sure, a basic understanding about it would be easy and achievable.