Method not being called from another class

The isOld method tests if int age is < 15. I've already complied the class and it comes with no errors, but when I try to call the method from another class it causes an error method isOld in class Pet cannot be applied to given types;

public static void isOld(int age)
   {
     if(age > 15)
     System.out.println("true");
    }

This is the PetRunner class:

import static java.lang.System.*;

public class PetRunner{

   public static void main( String[] args )
   {
      System.out.println("Pets");
      Pet cat = new Pet ("Lolo", 20);
      Pet dog = new Pet ("Buster", 40);
      System.out.println(cat);
      System.out.println(dog);
      cat.isOld();
      dog.isOld();