sort animals stl

#include <bits/stdc++.h>
using namespace std;

class Animal {
public:
    Animal(string name, int age): name(name), age(age) {}
    inline int getAge() const {
        return this->age;
    }
    friend ostream& operator << (ostream &out, const Animal &animal) noexcept ;
private:
    string name;
    int age;
};

ostream& operator << (ostream &out, const Animal &animal) noexcept {
    out << animal.name << ' ' << animal.age;
    return out;
}

class Dog : public Animal {
public:
    Dog(string name, int age): Animal(name, age) {}

};//*/
class Cat : public Animal {
public:
    Cat(string name, int age): Animal(name, age) {}
};

int main() {
    vector<Animal> animals = {
        Dog("azor", 11), Cat("thomas", 5), Dog("rex", 12)
    };
    sort(animals.begin(), animals.end(), [](const auto &fi, const auto &se) {
        return fi.getAge() < se.getAge();
    });
    for (const auto &animal : animals) {
        cout << animal << endl;
    }
    return 0;
}