How do I explain to my parents that I am 18!?

Okay so I turned 18 a few months ago and graduated high school and I finally want to start living. But my parents cannot seem to let go of the fact that I am an adult now and they need to learn how to treat me that way. My whole entire life my parents have been way overly protective and overbearing to the point where the first birthday party i ever went to was in my sopre year! This Summer i've been wanting to stay out late and hang out with my friends but my parents always flip a B*tch when I stay out past mid-night. My Dad has been out of the country for about 3 months so he miss my birthday and graduation. I don't hold it against him because thats just stupid but the thing is that now that he's back everything is the same when it's not. My mom's gotten a little over me coming home late but I just don't know how to explain to the both of them I can handle myself and I can't even bring up the courage to show them i got my ears pierced 2 weeks ago lol i've just been hiding it HELP!