He has not been charged with statutory rape, have you bothered to ask why? Zealots usually don't ever ask that question.
Here is a quote from a very recent article about this situation.
"During an interview, Araiza made it clear he’s not being charged for statutory rape because, in California, you can’t be charged if you had good reason to believe the other person was 18. Araiza said the unnamed woman clearly stated to him she was 18 and said it on video.
Clearly, the police believe that’s the case because he’s not been charged."
So the girl lied about the gang rape and lied about her age, which under California law is quite clear thus no rape occurred.
Oh, and San Diego State University just made a determination of "No Findings" on Friday regarding this matter.