And few lines could be thrown away, because IMHO last case will be never executed. And assignment operator is '='; '==' is comparison.
#include <iostream.h>
void main()
{
int age;
int myage = 14;
cout<<"plz input your age: ";
cin>>age;
if (age<myage)
cout<<"you are younger than me!";
else if(age==myage)
cout<<"you are the same age as me";
else
cout<<"you are older than me!";
}