I've been away from comics for years, just bought Justice League #1, 2018 the Scott Snyder run.

Barry Allen acts the way I'd expect Wally West to act. Hell Wally used to be more grown up than this. He's pitching a fit about being taken off of assignments, then going "Ew yeah you can have that assignment" A lot of it is the looks he has on his face, he's overly emotional in his reactions, not very professional or adult like you used to get out of Barry. I don't like it. I want a Flash who acts like a man, not a teenager.

Is this just a Scott Snyder thing or has his character been devolved?

Bad enough that they turned Wally back into a teenager then made him a murderer.