New to Java

Ok, I am new to Java and had an assignment to find the smallest number (age) of three given ages. I figured it out, but my code is quite cumbersome. For my personal knowledge, and better understanding of java, I would like to know how I can shorten/improve my code. Here's what I have:

import javax.swing.JOptionPane;

class Exercise67
{
     public static void main (String[ ] args)
     {    JOptionPane.showMessageDialog (null,
                    "Finding who is youngest out of three people.");
          new YoungestOfThree();
          System.exit (0);
     }    //======================
}    //########################################################


public class YoungestOfThree extends Object
{
     /** Find the youngest (lowest) age of three people. */

     public YoungestOfThree()
     {    String input = JOptionPane.showInputDialog 
                    ("Enter first age.");
          String input2 = JOptionPane.showInputDialog 
                    ("Enter second age.");
          String input3 = JOptionPane.showInputDialog 
                    ("Enter third age.");
          int age1 = Integer.parseInt (input);
          int age2 = Integer.parseInt (input2);
          int age3 = Integer.parseInt (input3);
          int counter = 1;
          int smallest = age1;
          while (counter < 4)
          {    if (age1 > age2)
                     smallest = age2;
               if (age2 > age3)
                     smallest = age3;
               counter++;
          }
          JOptionPane.showMessageDialog
                        (null, "The youngest age is: " + smallest);
     }    //======================
}

As I said, it works just fine, but if I was going to find the lowest number of say, 100 numbers, this would be far too cumbersome to use. Thanks for your time.