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.
Interesting post Andrew and I think I disagree only with the phrasing and not the general point. I think people can grow up, or maybe grow forward is a better term. This is done largely by controlling, or at least being self aware of, these fears and appreciating the joys. I do not think there is an expiry date for this. Ive met incredibly mature and well adjusted youngsters and elderly children.