I'm currently a junior in High School and I want to major in business administration after I graduate. The problem is, I have never taken a business course in my life and I want to make sure that this is the path I want to go to. It doesn't have to be at a university, but is there a way to enroll in a business course during summer so I can have a better idea on what a business career might look like?
Yes, there are absolutely summer business classes available. How you go about finding these courses will depend on whether you want to take an online course or a classroom course.
There are a bunch of great platforms that provide online courses at low or no cost to students of all backgrounds. I personally have taken a course through edX, which offers a variety of different business courses (at a variety of different levels). There's also Coursera, MIT OpenCourseWare, and many others.
Your in-person options for business classes may be a bit more limited, depending on where you live/where you're looking to take classes. To get an idea of what's out there, google "summer business course high school [location]" or "summer business classes high school [location]" and see what's nearby and open to high schoolers.
Another great option for learning more about what a business career might look like is to get some practical experience. Many companies have "job shadowing" programs where you can observe a professional at work. These aren't usually paid positions, but they can be great learning experiences, and often give you a better sense of what day-to-day life might be like in a career than taking a class in it would. The same thing applies to internships, which can be paid (and are usually of a longer duration than job shadowing programs).
Of course, you might want to take a business class anyway so that you can better understand what's going on when you're shadowing or interning, but I would highly recommend looking into getting this practical experience, in addition to the theoretical/abstract experience you'd get from a course in business administration.