Case
Having authority as a young teacher

When I first began assisting in the classroom, I felt as though most of my students saw me as their friend or older sibling rather than an authority figure. Although this was good in that it allowed them to open up to me and feel comfortable in the classroom, I worry how this'll impact my ability to hold authority as a teacher. Even some of my coworkers mistook me for a student at first, regardless of my professional attire. What can I do to come off as more mature and firm?

Solution #1
It makes sense that you would want to find a middle ground in the classroom between remaining authoritative and friendly. From the start of the school year, you can convey a more mature and firm approach by speaking assertively, setting clear boundaries, and displaying confident body language. Furthermore, you can build your credibility as a teacher by acting professionally, making wise decisions, and interacting with students and colleagues.
Solution #2
Age does not define value. If you walk in confident, can help and teach students, and set yourself to be the authority figure they need, age will be overlooked. Although they might first see you as young and easier to disobey, prove yourself to be powerful and do not let them overlook you.
Solution #3
Something you can do to continue to show authority is keep the rules of the classroom on the topic of mind consistently. If the students see the rules often and are reminded, they will be less likely to overstep and ruin some of their privileges.