I'll let you in on a little secret.
No one grows up. Everyone has the same sense of joy and fear and ego they have had since they were first conscious of themselves. People have different demands made of them in life, some by themselves, some by circumstance and some by expectation but the idea that because you're doing something with your life someone else isn't doing doesn't mean you aren't 'growing up.' I'm not going to stop doing silly voices to my husband to make him laugh just because I'm 30.
Hmmm I can't say I disagree but I do recall you not approving of that trait of me. 
That's because you are regressing
In all seriousness, I'm not saying that no one ever 'grows up'. I'm just saying that there isn't really a definitive measure for what it means to be an 'adult'. It does mean taking on responsibility and if you have children or a partner, care for others but it doesn't require a fundamental shift in who you are as a person. Too many people think you have to throw fun, awe, fear and everything else out the window or that your best role-model for an adult is someone that you are not. Those who often shout 'grow up' tend to mean 'grow up like me.'
