Do you have to be huge to be a security guard?

No. a buddy of mine is a SG here. He's old and out of shape but has a background in law enforcement so they signed him up no problem. In most countries you have mandatory security training, there are lots of female security guards as well. You should be able to handle yourself but in most cases you just observe and call for police. You're kind of an expert witness sort of thing. You're not there to confront just to report.