How to make conditions with IF statement right?

I have question about my IF statement, it just doesn’t work 😀
I want to check ID, age and salary, if it’s bigger than 0, but my code just ignore that, would like to change 0 to some meanings like – if age <= 0 set age = 21 etc
Will glad to see your answers.
Thank you!

class Person
{
    private int _age;
    private string _firstName;
    private string _lastName;
    private int _id;

    public Person(int age, string firstName, string lastName, int id)
    {
        _age = age;
        _firstName = firstName;
        _lastName = lastName;
        _id = id;
    }    
    
    public int GetAge()
    {
        return _age;
    }
    public void SetAge(int age)
    {
        if (_age == 0)
            _age = 21;
        else
            _age = age;
    }
    public int GetId()
    {
        return _id;
    }
    public void SetId(int id)
    {
        if (id > 0)
            _id = id;
        else
            _id = 1;
        
    }
    public void Print()
    {
        Console.WriteLine("Age: {0}\tFirst name: {1}\tLast name: {2}\tID: {3}", this._age, this._firstName, this._lastName, this._id);
    }
}

class TestInheritence
{
    public static void Main(string[] args)
    {
        Employe[] employees = new[]
        {
            new Employe(21, "John", "Watson", 0)
        };
        employees[0].Print();
    }  
}

>Solution :

It is because you don’t use the setters which have the if statements, you set the variables directly.
So instead of

_age = age;

You should use

setAge(age);