is this movie ok for a 8 year old?

Totally okay.

As long as he's an edgy 8 years old.

DC make pretty shitty movies so no

My guess is that not only will he be bored as hell, he's going to be angry that its not what he expected and will silently resent you for days afterward. Thanks for nothing, MOM. Because this looks like almost purely a character study, with lots and lots of talking. Maybe a scene of him getting beat up...before some more talking. Just...SO much talking. At least from an eight year old's perspective, I imagine.