I stay in South Africa, if the girl is 15yrs old and the guy is 21yrs old they both concented to the sex. Can the girls parents press charges on the guy?

At certain ages, the minor child, can not legally consent,

So yes parents can press charges.

A child can not give permission to have sex.

"stagetory"? Perhaps you mean "statutory", as in "statutory rape"?

And, I assume, "concent" means "consent".

The age of consent in South Africa appears to be 16.

The age of consent in South Africa is 16. Its called age of consent because a person under the age of consent cannot legally give consent. So yes, her parents could (and should) press charges.

As another answer has said, the age of consent in South Africa is 16 years old. Here is a link with many areas and explanations:
Ages of consent in Africa - Wikipedia, the free encyclopedia
The parents can press charges on the guy, if they wish.