Try This

System.DateTime FirstDate
System.DateTime SecondDate
System.DateTime OriginalDate
int year,month,day,monthDays;
year=month=day=monthDays=0;

OriginalDate=FirstDate;
monthDays=System.DateTime.DaysInMonth(OriginalDate.Year,OriginalDate.Month);

year=FirstDate.year-SecondDate.Year
if(SecondDate.DayOfYear<FirstDate.DayOfYear)
{
    year--;
}

FirstDate=new
System.DateTime(SecondDate.Year,FirstDate.Month,FirstDate.Day);
month=Math.Abs(FirstDate.Month-((SecondDate.Month<FirstDate.Month) ?
12+FirstDate.Month : FirstDate.Month));

if(SecondDate.Day<FirstDate.Day)
{
    month--;
    day=monthDays-FirstDate.Day-SecondDate.Day;
}
else
{
    day=SecondDate.Day-FirstDate.Day;
}