Mature or not?

I've been 18 for a few weeks now.
Some years ago, when I was 10 or 12 I was thinking what it would be like when I'm 18. I thought I'd be an adult, that I'd always know what to do and so on.
And now, how do I feel. I feel more irresponsible than ever before. Less confident. I don't know what my future life should be like. I often doubt my decisions are the right ones.
I try to avoid serious and global topics and concentrate on my own life and my petty problems.
Before I had strong opinions on politics and all the world problems and I thought I knew the remedies. Now I acknowledge I'm not sure even in my own life.