zanzibar: Here is a local news article about the arrest and allegations:
Please be aware that an arrest is not a conviction, and that initial reports are not always representative of what truly occurred.
For instance, what is the evidence that he even actually had sex with the girl? If it is only testimonial then it is for a jury to determine whether it is reliable evidence.
These are typically difficult cases. She was on OK Cupid, which according to the article is an adult dating site. So questions about his awareness of her age must be fully examined in an unbiased court of law.
Her reliability as a witness should be important here - but one must wonder why she was writing about the incident on her profile, and not talking to her parents or other authorities. There is the danger of the investigators "shaping" the story in these situations (see the Duke rape incident, or the Fells Acres Day Care Center preschool trial/scandal).
(OK Cupid are the same group that successfully brought the resignation of Brendan Eich)
The adage "innocent until proven guilty" is sadly not always true in the US, if it ever really was. The power of the prosecution, and the extreme variability of penalties, often force even the innocence to accept plead deals rather than run the risk of draconian punishment.
This works the other way as well, where serious offenders get lighter sentences when prosecutors decide they want to clear the docket. A recent case of this involved a murder/shooting on a naval base.
"Savage was incarcerated in various Virginia jails and North Carolina prisons for almost four years after being arrested in November 2005 in connection with the death of a man found shot to death on an interstate on ramp in Charlotte, N.C. [...] Court records say prosecutors had planned to seek the death penalty against Savage if he didn't settle his case with a guilty plea. He was released from prison in December 2009."
So, it appears whether the crime deserves 5 years or the death sentence isn't determined by a judge anymore, but rather by a prosecutor.