There's no single answer to how many credit hours constitute senior status in a 64-credit program. The number varies significantly depending on the institution. Some schools might consider you a senior after completing 90% of the program's required credits (around 58 credits in a 64-credit program), while others might require you to have completed a specific number of credits within the major or have a minimum overall cumulative GPA.
To find the answer:
You need to check the specific requirements for senior status in your college's or university's student handbook, academic catalog, or by contacting the registrar's office or your academic advisor. They will have the definitive answer for your particular program and institution.