I only act immature around my friends. We know each other well enough where we dont have to take each other seriously at all. In that regard, I can be immature. For the most part, I act responsibly.
Mental maturity, most likely around my age. I used to think I held a higher standard for myself, but I probably am the same as my friends.
[Edited on 01.08.2013 5:21 AM PST]