Oh my dear (((((((((((((Kaika)))))))))))))
With increasing age comes some more responsibility (like drinking, voting, driving etc) but it doesn't mean that you're an "adult". I've seen teenagers who act more mature than 30-40 year olds, and vice versa...
Why would I be disappointed with you?
Yes, you turned 18 - congratulations. But I expect nothing less than to be YOURSELF from you - that's it. Same thing for my baby sister, who turned 18 back in March!
I mean, I'm 6 days away from being TWENTY-THREE (23!)!! Most people here wouldn't guess that I was that young, because I can act more mature than my age at times...
But my IRL friends call me CHILDISH! Because I love acting like a kid and having fun ... I guess reliving my childhood and making up for it now.
I still can't balance a checkbook. I can't manage my finances if my life depended on it! I still eat junk food and don't eat proper meals a lot of the time. I don't drive. I used to drink too much and then quit drinking alcohol altogether! I don't like cleaning. I couldn't care less for "adult" conversations all the time, and I don't give a rats *** about politics and the economy.
If people want you to "grow up" ... then you do it at your own pace! You aren't going to wake up one day and have changed that dramatically from the day before! It just won't happen!
You're experiencing the societal pressure to "grow up" and all I'm going to say here is that you WILL be getting more responsibilities now that you're older. But you don't have to ACT differently until you want to or actually *need* to! Me, I'm terrified of the "real world" and getting a fulltime job. I like being a student, less pressures... I guess I'm hiding at university, along with a lot of other people.

Love ya bunches kid.