The ideas of adult and mature are so overrated. Usually when you get told to "grow up" its because you're making a joke or acting juvenile. Is that so bad? Adult is boring, no fun, serious. Becoming adult means losing that playful mischieviousness you grew up with and being able to sit in a cubicle like everyone else going through life like a robot. "Grow up" just means "join us in boring dull delerium because we gave in to the pressure and "grew up" as our parents told us so you have to too- join us in the mature boring world of being an adult".