I don't think it is OK to have a statute of limitations on rape, because people who committed it before there was a way to use DNA as evidence will get away with it, when they should be punished.
There are many rapists who acted before we were able to properly test DNA and use it as evidence in court cases. We now can test evidence from old cases. But those rapists will still go free because of the statute of limitation. They should be punished so they don't rape again.