User blog comment:Zolnir/Welcome To Beacon/@comment-108.16.0.12-20140802065104/@comment-96.254.157.84-20140802065729

1) Ozpin recognizes the White Fang as a threat, but he's smart enough to know that "shows of power" will only motivate the Faunus to side with the White Fang and push things further into a war.

2) Ozpin no doubt knows who Cinder is, but is allowing her to stay at Beacon for an obvious reason: Keep your friends close and your enemies closer. With Cinder in Beacon, he can keep a closer eye on her and potentially defuse the situation before it gets out of hand. And Cinder is smart enough not to do anything reckless under Ozpin's eye.

3) According to Monty, Cinder is older than the main cast, but only looks younger. Then there's the fact tha Monty let it slip that Cinder might have been Ozpin's student, meaning she's been to Beacon before. I'd gauge her around her mid-20s at best.