int age;        //Declare an Int variable to hold your age

void setup() {

  Serial.begin(9600);      // Initialize Serial Port

}

void loop() {

  Serial.println("How old are you? ");        //Prompt User for input

  while (Serial.available()==0){}             // wait for user input

  age = Serial.parseInt();                    //Read user input and hold it in a variable

  // Print well formatted output

  Serial.print("You are ");                 

  Serial.print(age);

  Serial.println(" years old.");

  }