public static int PromptInt(string message)
    {
      Console.Write(message);
      var input = Console.ReadLine();

      if (String.IsNullOrEmpty(input)) return 0;

      var isNumber = int.TryParse(input, out var age);
      if (!isNumber) return -1;
      if (age > 200 || age <= 0) return -1;

      if (age == -1)
      {
        Console.WriteLine(age + " is not a valid number.");
      }
      return age;
    }