AgeCalculator.cs

public static string ToAgeString(DateTime dob)
        {
            DateTime today = DateTime.Today;

            int months = today.Month - dob.Month;
            int years = today.Year - dob.Year;

            if (today.Day < dob.Day)
            {
                months--;
            }

            if (months < 0)
            {
                years--;
                months += 12;
            }

            int days = (today - dob.AddMonths((years * 12) + months)).Days;

            return string.Format("{0} year{1}, {2} month{3} and {4} day{5}",
                                 years, (years == 1) ? "" : "s",
                                 months, (months == 1) ? "" : "s",
                                 days, (days == 1) ? "" : "s");
        }

        public static string AgeDiff(DateTime bigger, DateTime _smaller)
        {
            DateTime smaller = _smaller;

            int months = smaller.Month - bigger.Month;
            int years = smaller.Year - bigger.Year;

            if (smaller.Day < bigger.Day)
            {
                months--;
            }

            if (months < 0)
            {
                years--;
                months += 12;
            }

            int days = (smaller - bigger.AddMonths((years * 12) + months)).Days;

            return string.Format("{0} year{1}, {2} month{3} and {4} day{5}",
                                 years, (years == 1) ? "" : "s",
                                 months, (months == 1) ? "" : "s",
                                 days, (days == 1) ? "" : "s");
        }