I'm starting my new job in a few weeks and I am TERRIFIED! Any advice?

I'm starting a job in a few weeks, my second one ever, and I am TERRIFIED! I'm mostly scared because I'm in introvert and people scare me and make me nervous, but also because I'm only 18 and my job has people over the age of 40. I feel like I'm going to be seen as a child! I. am. TERRIFIED! Someone help me get over this fear and help me feel better about this please!!!