High School Senior Interested in Investment Banking – How to Start Learning?

My little brother is currently a senior in high school and has mentioned that he’s interested in eventually going into investment banking. I know recruiting timelines are very early, so I was wondering if there’s anything he can start doing now just to learn the basics and gauge whether it’s something he actually likes.

For context, I’m 5 years older and work in the real estate credit space, so I don’t really have much insight into what the IB world looks like day-to-day or what people typically do early on to prepare. Just coming here for advice.

Are there any basic courses, books, or resources he could look into at this stage? Not necessarily to “prep for recruiting,” but more to understand what investment banking actually is and whether it’s a good fit. Thanks.