System.Globalization.Calendar.GetYear C# (CSharp) Method

        public abstract int GetYear(DateTime time);

        /// <summary>
        /// Initializes a new instance of <see cref="Age"/>.
        /// </summary>
        /// <param name="start">The date and time when the age started.</param>
        /// <param name="end">The date and time when the age ended.</param>
        /// <param name="calendar">Calendar used to calculate age.</param>
        public Age(DateTime start, DateTime end, Calendar calendar)
        {
            if (start > end) throw new ArgumentException("The starting date cannot be later than the end date.");

            var startDate = start.Date;
            var endDate = end.Date;

            _years = _months = _days = 0;
            _days += calendar.GetDayOfMonth(endDate) - calendar.GetDayOfMonth(startDate);
            if (_days < 0)
            {
                _days += calendar.GetDaysInMonth(calendar.GetYear(startDate), calendar.GetMonth(startDate));
                _months--;
            }
            _months += calendar.GetMonth(endDate) - calendar.GetMonth(startDate);
            if (_months < 0)
            {
                _months += calendar.GetMonthsInYear(calendar.GetYear(startDate));
                _years--;
            }
            _years += calendar.GetYear(endDate) - calendar.GetYear(startDate);

            var ts = endDate.Subtract(startDate);
            _totalDays = (Int32)ts.TotalDays;
        }