Swift Code: -

class Person { var age: Int = 0

init(initialAge: Int) {
    // Add some more code to run some checks on initialAge

    if initialAge < 0 {
        self.age = 0
        print("Age is not valid, setting age to 0.")
    }else {
        self.age = initialAge
    }

}

func amIOld() {
    // Do some computations in here and print out the correct statement to the console
    if self.age < 13 {
        print("You are a teenager.")
    }else if self.age >= 13 && self.age < 18 {
        print("You are young.")
    }else if self.age >= 18 {
        print("You are old.")
    }
}

func yearPasses() {
    // Increment the age of the person in here
    age += 1
}

}