CSharp Solution

using System;

class Person
{
    public int age;

    public Person(int initialAge)
    {
        // Add some more code to run some checks on initialAge
        if (initialAge > 0)
        {
            age = initialAge;
        }
        else
        {
            Console.WriteLine("Age is not valid, setting age to 0.");
            age = 0;
        }
    }

    public void amIOld()
    {
        // Write code determining if this person's age is old and print the correct statement:
        if (age < 13) Console.WriteLine("You are young.");
        else if (age < 18) Console.WriteLine("You are a teenager.");
        else Console.WriteLine("You are old.");
    }

    public void yearPasses()
    {
        // Increment the age of the person in here
        age++;
    }
}

class Solution
{

    public static void Main(String[] args)
    {
        int T = int.Parse(Console.In.ReadLine());
        for (int i = 0; i < T; i++)
        {
            int age = int.Parse(Console.In.ReadLine());
            Person p = new Person(age);
            p.amIOld();
            for (int j = 0; j < 3; j++)
            {
                p.yearPasses();
            }
            p.amIOld();
            Console.WriteLine();
        }
    }
}