Any advice for me

Hey, so I'm not old enough to join yet, but I am a high-school student who is working VERY hard to get in. I'm in public safety at my high school, and I'm learning Spanish and Arabic. I'm going to get an accounting degree and then be a cop until I'm 26. I'm applying to the FBI (dream agency) US marshals and ATF

What should I expect and prepare for

(In case you're wondering, I made a 50 in the official fbi jobs.gov practice exam)