Yohji Yamamoto says “Start by copying. Copy copy copy copy. At the end of the copy, you will find yourself.” That sounds like the long and short of being an adolescent. We copy the people we wanted to be, people we idolised.
Being an adult is a little different. The teenage personas we took on were expected to end, and we are expected to provide some justification for things we do or choose. Responsibilities come our way. You should have some semblance of who you are, but now you need to learn to negotiate with the world around you.