Experience and Maturity (or the lack of both :D)

Yes, I know. I seriously need to learn how to come up with better titles for my posts. "Experience and Maturity" - seriously??? Sounds like a bloody platitude. I'm the very last person you should take advice from, believe me. This brings me to my point (I'd bet the word "finally" is going through most people's head right now :D)
Can someone be mature without doing stupid things? The inspiration behind this very irrelevant thought is a conversation I had had with one of my friends. (I have these sort of conversations surprisingly often, given that my EQ is best left undisclosed) During the course of this particular conversation, I picked up on the fact that I may tend to come across as "boring" to most people. (@friend: If you are reading this, no need to clarify your position. I know that "boring" isn't in your description of me ;D) That's true, and I really don't give a damn about it. What was also implied was that I seemed to be "mature" or I had a "level-head". In short, I was the steady, stable guy, as opposed to the "wild" one. Those particular words got me thinking (a sure sign of trouble, isn't it :P) - Can someone be mature without having done stupid things? By "stupid things" I mean the sort of things 20-year-olds do behind their parents' back - dope, booze, sex etc. (Just to clarify, my view on these things is very liberal - You want to do something, go ahead and do it. None of my concern, and I'm nobody to judge) Do you need to actually do these things and then stop doing them, (paradoxical, right?) before you can say that you have grown wiser? Does the saying "wise men learn from others' mistakes" apply here? Or do you need to learn from your own mistakes?
If it's the latter case, I guess I have the maturity of a toddler. (coupled with the emotional range of a teaspoon, it makes for a great combination - just ask some of my friends :D) Heck, even if it's the former, I don't think I've actually learned much - I still feel like I'm fifteen years old, at best. I most definitely don't look any older.