Promoted at work and nervous

I started my job in property management right out of high school when I was 18. I was hired as a leasing consultant with no prior experience, and after 6 months I was promoted to Assistant Manager. I have been an assistant manager for what would be 2 years in May. I am now being promoted to Community Manager. Of course it’s what I’ve wanted and been working for. I know I’m very good at my job and I work for a great company that I’ve very glad sees my potential. But I am nervous about being a manager because I’m only 21. This is a 200+ unit property that employs 4 people total. I am worried that they are not going to take me seriously because of my age. I am worried that other managers are not going to take me seriously. I’m worried about what people are going to say about me. That I’m too young, I’m not ready, I don’t have enough experience, etc. my regional manager is VERY supportive of me, but I don’t want to fail. Does anyone have any advise? How can I be a good boss at a young age? How can I make sure people respect my authority? How can I make sure I’m being the best I can be at my job?