How can I act more mature and like an adult?

You act like this because you really are still a kid, and that's okay! You're only young for a short part of your life, so why give it up sooner than necessary? Act like this while you still can and be yourself! Have lots of fun and don't worry about acting older. You'll have the rest of your life for that!:)

All folks to a particular quantity difference the way in which we behave relying on who we're with. I am a mature grownup, but if operating with more youthful folks, you should be extra on their degree as it's so much less complicated to socialise that approach. With household I act one of a kind to the way in which I do with my peers. I have a significant part and a amusing part. It is only a aspect of being an grownup. Have you attempted discussing the extra highbrow matters along with your peers? Perhaps you ought to uncover a different set of peers of you age who're interested within the identical matters.

it's not a sin to be immature.
in another word it's cute ;)

Be more mean? Plenty of people are like yourself and mature. Carry yourself with more confidence and be more knowledgeable..

Maturity isn't a matter of preferences, it's matter of mentality :) Carry yourself with confidence, talk about things you know/have seen/experienced, crack a cheeky joke. I know it's not about appearance and I don't know what's your style, but chic clothes, heels, bit of jewelry do the trick sometimes.