Tell me, how do you define mature? As you have to live for your work, always being serious and do not have a hobby that you're crazy about? Like, if you like riding and can talk about horses with pure happiness and love, you're immature, because it MIGHT seem to be childish to love horses that much?
In my humble opinion being mature is none of this. Taking the consequences what you've done with dignity and without blaming others, NOT looking down on others just because they love something, more like. (Like, I do not understand what some like about Justin Bieber, but I would never classify them as "lower beings" or "idiots".) Again, this is just my opinion.
Ps. - Maturity doesn't depend on age. One can be sixteen, cosplayer and mature, while the other thirty, I-don't-have-any-fun-in-my-life-because-I-am-oh-so-mature.