Can a person that is 20 year of age can they have enter course with a 16 year old and get charges preset against him even if she wanted to even in the state of Mississippi?

The age of consent is 16 in Mississippi so sex would be legal since she is old enough to give consent. If she had not been the age of consent though it would have been illegal since her saying she wanted to would not mean she could give consent. It's always the adults responsibility to know how old the person they sleep with is and if it is legal. Saying the minor wanted to or that you did not know her age does not make it legal.