I'd recommend you find someone who's worked as an actual broker and offer to buy them lunch in exchange for them telling you exactly what they did as a broker and giving you a broad outline of the industry. Use LinkedIn to see if you know anyone at the 1st or second level who fits this description or use your school's alumni network and just make some cold-calls/emails, letting them know you're a college freshman and you'd value a few minutes of their time to help you learn. Be humble, don't tell them your plans to retire at 30 after opening a brokerage, just be a sponge and soak up all you can. Do this frequently with every great idea you come up with during school, you'll bounce around and probably end up with 20 different entrepreneurial plans, some in opposite directions from one another. Take the time to research and talk to people who've worked in those areas each time. You'll learn a ton and if you're as motivated as you sound you may very well find the seed of an idea. The key is humility. Come in saying you're super motivated and smart but know what you don't know and you want to learn more. That attitude eliminates a lot of the "you've got a lot to learn, son" response you'll tend to get with the way you came across here. Specific to being a broker, I'll give you one tip. Brokers add value in very illiquid things, most of which don't trade on a regulated exchange or where the majority of actual volume is OTC. Think uranium, coal, shipping.... It's not out of the realm of reason that someone with no experience and no licenses can start a lucrative business brokering these kind of items; I was able to.
A brokerage is not Trader Joe's. They probably are subject to a million rules about how/what they can advertise.
Not to mention it's a competitive field with firms investing billions in their technology and distribution platforms. I would be shocked if there's an underserved niche.