Thanks for the question. According to a listing on USAJobs.gov for a "Customs and Border Protection Officer" the entry-level requirements are:
"a. Three years of general work experience that demonstrates the ability to meet and deal with people and the ability to learn and apply a body of facts; OR
b. A bachelor's degree from an accredited or pre-accredited college or university; OR
c. A combination of successfully completed post-high school education and general work experience. This will be calculated using your resume and unofficial transcripts submitted with your application."
So, you'd need around 3-4 years of work/education experience as a minimum requirement. For example, a two-year associate's degree and one year of experience as a security officer may meet these requirements. Another example could be earning your bachelor's degree and then applying. There is also a 30 day pre-academy orientation requirement followed by a 17-19 week academy training in Georgia.
These are the most basic requirements, but here's a link to the job description for more information: https://www.usajobs.gov/GetJob/ViewDetails/440021600/
Best of luck!