Just Be Yourself
The day before I turned eighteen, I cried. I felt that my childhood was over. When I was younger, I wanted to be older, but once I turned twelve, I wanted to stay a kid forever. Problem is, in six years, I was literally scared. I was sad. I was troubled. I don't exactly know what was wrong with me. It felt like it was the end of my world as I knew it. I prayed, I immersed myself in much childhood nostalgia, and then I went to bed.
Next day, I woke up, and I felt normal. I was still myself. I could still play around. I could still enjoy all my favorite childhood things. I felt so silly acting the way I did. Fortunately, I had a family that didn't say something like "You're eighteen now, GET OUT." Of course, I had a few more responsibilities, and graduated highschool, different things, but overall, you don't have to change much. You can still be yourself.
I still don't go to wild parties, drink, smoke, curse or anything just to BE GROWN. There's not a specific persona of an "official adult" you have to channel once you cross the threshold. Just pray about it, take on your new responsibilities, be yourself, and have fun!
(PS, I had my senior pics taken at a playground to show the connection to my childhood was not lost :))