Basically, anyone with the $$$ can take the CISSP exam at any time. Getting the full CISSP certification has actual professional requirements that must be met. Have a look at the CISSP exam registration form and endorsement form for additional useful information.
Welcome to TE. Have checked the CISSP Candidate Information Bulletin? Also https://www.isc2.org/steps-for-certification.aspx has a step-by-step on the process. Is something is not clear as away and we'll do our best to clarify.