"string is not a type" in namespace

I write a program in c++ with two files.

main.cpp

#include "var.hpp"
 #include <iostream>
 using namespace std;
 using namespace YU;
 
 int main()
 {
     string god = "THL";
     age = 10;
     cout << age << endl;
     cout << god << endl;
     return 0;
 }
 

var.hpp

#ifndef __VAR_H__
 #define __VAR_H__
 
 #include <string>
 
 namespace YU
 {
     int age;
     string name;
 }