It looks like we're having another confusion, this time between necessary and sufficient conditions. Physical maturity is just a threshold. (And 13 would be just an early phase of that maturation process.) It isn't sufficient to prove, much less excuse, anything. It's just a threshold for beginning to make the kinds of arguments a defense attorney might make: that the younger party consented or indicated consent, or that the defendant isn't constitutionally attracted to children. Below that age threshold, such arguments can't even begin.

If I understand your question, the answer is: No, physical maturity by itself proves nothing. Physically mature people are raped all the time, and their rapists are rightly put away.