I once taught a creative writing class for adults - very mixed ages. What I found very hard was that some people, often very keen, produce writing that was almost incomprehensible and couldn't accept that they needed to study and employ basics like maintaining their objective in a paragraph (or, indeed, how to use paragraphs) writing clear, grammatical English so that their readers could understand and all the usual, basic techniques. In fact, even the concept of writing for a reader was a new idea for them.
Some people could see this, and worked hard at improving, and did, but there were always one or two who thought they were God's gift to literature, and that I, and the publishers who had rejected them, were part of some sort of conspiracy.
I did have some lovely, talented students too, who listened, worked and blossomed, and that made it worthwhile. But I would much rather teach sixteen year olds, any day. Or not teach at all, like now! 