C2662 Cannot convert "this" pointer from const xxx "to" xxx & "

C2662 Cannot convert "this" pointer from const student "to" student & "

Operating environment:
vc2010 learning version

example:

#include <iostream>
#include <set>
#include <functional>
#include <algorithm>

using namespace std;

class student
{
public:
	student(int age)
	{
		this->age = age;
	}

	bool operator < (const student &right) const
	{
		return this->age < right.age;
	}

	int getAge()
	{
		return age;
	}

private:
	int age;
};

int main()
{
	set<student> setStu; //等同于 set<student, less<student>>
	setStu.insert(student(18));
	setStu.insert(student(19));

	for(set<student>::iterator it = setStu.begin(); it != setStu.end(); it++)
	{
		cout<<it->getAge();
		cout<<" ";
	}
	cout<<endl;

	system("pause");
	return 0;
}

The error is reported as follows:
error C2662: "student :: getAge": Cannot convert "this" pointer from "const student" to "student &"

Reason:
it is const and getAge is not const, because it is constant, but it may be wrong if it involves changes

Solution:
Modify:

int getAge() const
	{
		return age;
	}

Running results:
18 19