using System;

public class Program

{

    public static void Main()

    {

        DateTime fileDate = new DateTime(2013, 5, 1);

        DateTime fileDateNewer = new DateTime(2014, 1, 1);

        GetMonthDifference(fileDate);

        GetMonthDifference(fileDateNewer);

    }

    public static void GetMonthDifference(DateTime fileDate)

    {

        DateTime currentDate =  DateTime.Now;

        DateTime eighteenMonthsAgo = currentDate.AddMonths(-18);

        if (eighteenMonthsAgo > fileDate)

            Console.WriteLine("{0} is greater than or equal to 18 months ago", fileDate);

        else

            Console.WriteLine("{0} is less than 18 months ago", fileDate);

    }

}