class example created by dzsquared - https://repl.it/Ewys/0

class example.cs

class Person {
    public int age;     
	public Person(int initialAge) {
        // Add some more code to run some checks on initialAge
        if (initialAge < 0) {
            Console.WriteLine("Age is not valid, setting age to 0.");
            this.age = 0;
        } else {
            this.age = initialAge;
        }
     }
     public void amIOld() {
        // Do some computations in here and print out the correct statement to the console
         if (this.age < 13) {
             Console.WriteLine("You are young.");
         } else if (this.age >= 13 && this.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
         this.age += 1;
     }
}