One of your best contributions so far. I have the feeling what most people mean when they say "grow up!" is to accept being trapped by the expectations of others, to embrace resignation as a mode of existence, to stop trying to change things and accept the world is going to shit and just take care of numero uno.
What do children want? They want everyone to be happy, that none suffer, that things are fair and just and they will try to make it happen. They want to learn. Adults? Not so much. Being "grown- up" according to modern parlance is definitely overrated.
Maybe being grown up should be about realizing what we wanted as children, making it happen, maybe it is. Maybe some people just want to conform to what they see as "grown-up" so badly they make themselves that way. But I repeat myself....
Great post!