Celebrating you 20th birthday is like celebrating the beginning of a whole new life. You are no longer in your teenage years, and can officially call yourself an adult. Pretty much anything goes on your 20th for all of those reasons.
Be a Kid Again
A great way to celebrate your 20th birthday is to relive being a kid again. You have the other nine years to celebrate your decade, so use this birthday to get away with acting like a child one last time. Go to the park, play on the swings and in the dirt. Eat ice cream and candy. Relax and play.
Play games that you enjoyed as a child or teen such as softball, badminton or soccer at the park. Set up different games, so all your friends can participate in them.
Not Quite Old Enough
Since you are not 21 years old yet, you can throw a party similar to the one you will have next year, only tone it down a bit. Have all of the classic alcoholic drinks like margaritas and pina coladas, but make them non-alcoholic. It will be like a pre-party for the following year.
Throw a 20s Themed Party
Your "golden" birthday is when your age falls on the same day as your birthday. Why not put a twist on that and throw a 1920s themed birthday party for yourself on your 20th birthday? Send invitations saying men should dress as historic gangsters and women should wear flapper dresses. You can spend the day getting prepped in costume, hair and make-up, and then celebrate when the night arrives. Hire a jazz band, have someone in costume at the front door checking for guns when people walk in, and serve sparkling cider to your guests in place of champagne. Make sure all decorations flow with the theme, and consider doing things in groups of "20." Maybe you could only invite 20 guests or have 20 food selections.
Do Something Thrilling
Since you have entered a new phase of life, do something you have never done before or that you are afraid to do. Go bungee jumping, scuba diving or skydiving to celebrate your new decade and kick it off with a bang. If there's something you've always wanted to do but you've never made time for, do it on your birthday. Ask a couple close friends to do it with you.