I dunno, I feel like Dostoevsky hits perfectly around high school. I enjoyed Crime and Punishment around 9th grade, but tried read some Dostoevsky as an adult, and it really reads like young adult luterature.
I only learned to appreciate Tolstoy as an adult though - it was extremely boring for me as a teenager barring some smaller pieces
Tolstoy is pretty heavy on religious perspectives on moral question. That's probably why I would be boring to a teen. And I totally agree that books like C&P are perfectly readable for young adults. Some people overemphasize the part of analyzing hypothetical symbolism instead of "just" enjoying the story.
The Brothers Karamazov reads like young adult literature? Hard disagree there. Maybe in terms of how navel-gazey it is, but the themes are not at all young adult.