It will start without you knowing it. It will creep up on you in tiny increments until there is no turning back. And you realize now it's smart that it happens in tiny steps, because if you knew that it was going to happen, you're not sure you would think yourself ready. You would find an excuse to dislike it, look for a way to prevent it.
One day your feelings will get hurt and instead of sending an angry email you will decide to sleep on it. You will say sorry first when it's your fault, and you will mean it when you say it. You will wear more sunscreen and a little less sparkly eyeshadow. You find that you give as many handshakes as high fives. You will find that life suddenly begins to eat up your time and daily two hour phone calls about every detail of your best friends life no longer happen. All of a sudden not every lip gloss you own will be named after a berry. You will learn that sometimes people are better off not knowing, and you will be able to keep your secrets secret. You won't apologize for leaving the party early, for not dating someone who uses large stacks of pornography as a nightstand or for things out of your control.
You will floss more.
When your friends talk of their houses, they are no longer referring to the ones their dad built them in a tree. They own their own. They drive cars without rust, wear high heels without teetering and tell you they love you at times other than 3am. They will have offices and responsibilities and suddenly you will know that you can count on them to be there not just for the party, but for the funeral. They will not always know what to say, but they will know that they need to be there. And they will know that is enough.
Suddenly you will know more married people than not- and it doesn't scare you.
You will find yourself a part of a club that you didn't know existed. A club where people talk about 401k's and wine and all the excellent television found on a Friday night. And at first you are reluctant to join the club, but you know you can't go back. So you stay, not always knowing what to say or how you fit in but then you realize being here is less stressful, less dramatic. You find that you feel... relieved, happier to know that there is a life outside the world you knew. You realize this new group also talks about goals and the future and they say things like 'when we do this' not 'if we can ever do this'- and that comforts you. They own plants that don't die, ideas that are theirs and pots that have matching lids.
But sometimes, you will feel wistful. The great stories of dancing all night and drinking from contraptions held together with duct tape will feel over. You will miss the late nights but can now recall the painful mornings. You will fondly remember spending all your money on shoes and clothes but now like the idea of a home and savings accounts and pots with matching lids. You will miss knowing every single detail of your closest friends lives, but then you realize, you are starting to learn the details of your own.
One day without realizing it, you will have become an adult.