It's barely a question in poetry. Verse can be light, but nobody I asked thought of poetry for, say, high school students vs. poetry for adults. Billy Collins did "Poetry 180" and literally everybody in the book was a poet-for-adults who'd written poems that a kid would like. You know that's true for most of my poems, and it's just as true for a lot of my friends. People like Barbara Hamby and David Kirby.
Really dense and difficult poetry isn't so much for adults only as it is for people who like puzzles. A smart kid would get a kick out of someone like John Ashberry who has an enormous wingspan that casts a giant shadow but is also very playful.
The funny thing about YA fiction vs. poetry is that I'll usually give a generic kids' novel set mostly in a mall frequented by vampires a few pages to get going but when I read a line of poetry like this -- "Even if the gust that undoes us/is dimmed in oblivion" -- that's it for me.
Having said that, now I'm wondering if patience separates Fiction/YA fiction. I tend to be patient with Fiction, less so with YA novels. I have a feeling that the former could go anywhere but I usually know right where the latter is headed.