I have been asking myself this question as far as I could remember, and as I get older, the answer always changes. The criteria for being a "grown-up" is different for everyone because we all have unique expectations based on our experiences.

There are often times when we see a "grown-up" with "younger" characteristics. Could this be because this person doesn't view themselves as one, therefore acts and appears such way, or is it simply because the person judging him/her has a solidified idea of what a "grown-up" should be like?

I believe being a grown-up is just a state of mind. A state where the amount of questions you have about yourself, life, and everything else is significantly lower than your past. A state where insecurities become non-existent, and everything seems to just make sense...