I agree with MassPackersFan that it's more about lack of confidence than it is about immaturity, although of course the two are related.
I don't know if our running back's twitters have anything to do with it. A lot of NFL players twitter, don't they?
As for players spouting off publicly about the system, the only ones I can think of are Charles Woodson and Cullen Jenkins, who are veterans, so that doesn't strike me as immature. I think Woodson's comments have been on the mark, and he is good enough and respected enough to say stuff like that. I'm less sure about Jenkins. With him, it may have been pure frustration.