Could a shorter person become a good Correctional officer?

My brother is 5'5. Him becoming a CO scares me. Someone might try and overpower him because of his size. He just received his BA in criminal justice...anyways.. As we all know the job market isn't the greatest these days. He's been looking for a job but hasn't had much luck. He works at Target and we all know target doesn't pay Sh*%! My Bro has a background in the Military too.