var EndDate = new DateTime(2022, 4, 21);

        var StartDate = new DateTime(1986, 4, 25);

        Int32 Months = EndDate.Month - StartDate.Month;

        Int32 Years = EndDate.Year - StartDate.Year;

        Int32 Days = EndDate.Day - StartDate.Day;

        if (Days < 0)
        {
            Months = Months - 1;
        }

        if (Months < 0)
        {
            Years = Years - 1;

            Months = Months + 12;
        }
        
        string Ages = Years.ToString() + " Year(s) " + Months.ToString() + " Month(s) ";

我只想这样做：

DateTime birthDay = new DateTime(1990, 05, 23);
DateTime age = DateTime.Now - birthDay;

这样你就可以计算出一个人的确切年龄，如果你愿意的话，可以精确到毫秒。

以下方法（从.NET类DateDiff的时间段库中提取）考虑区域性信息的日历：

// ----------------------------------------------------------------------
private static int YearDiff( DateTime date1, DateTime date2 )
{
  return YearDiff( date1, date2, DateTimeFormatInfo.CurrentInfo.Calendar );
} // YearDiff

// ----------------------------------------------------------------------
private static int YearDiff( DateTime date1, DateTime date2, Calendar calendar )
{
  if ( date1.Equals( date2 ) )
  {
    return 0;
  }

  int year1 = calendar.GetYear( date1 );
  int month1 = calendar.GetMonth( date1 );
  int year2 = calendar.GetYear( date2 );
  int month2 = calendar.GetMonth( date2 );

  // find the the day to compare
  int compareDay = date2.Day;
  int compareDaysPerMonth = calendar.GetDaysInMonth( year1, month1 );
  if ( compareDay > compareDaysPerMonth )
  {
    compareDay = compareDaysPerMonth;
  }

  // build the compare date
  DateTime compareDate = new DateTime( year1, month2, compareDay,
    date2.Hour, date2.Minute, date2.Second, date2.Millisecond );
  if ( date2 > date1 )
  {
    if ( compareDate < date1 )
    {
      compareDate = compareDate.AddYears( 1 );
    }
  }
  else
  {
    if ( compareDate > date1 )
    {
      compareDate = compareDate.AddYears( -1 );
    }
  }
  return year2 - calendar.GetYear( compareDate );
} // YearDiff

用法：

// ----------------------------------------------------------------------
public void CalculateAgeSamples()
{
  PrintAge( new DateTime( 2000, 02, 29 ), new DateTime( 2009, 02, 28 ) );
  // > Birthdate=29.02.2000, Age at 28.02.2009 is 8 years
  PrintAge( new DateTime( 2000, 02, 29 ), new DateTime( 2012, 02, 28 ) );
  // > Birthdate=29.02.2000, Age at 28.02.2012 is 11 years
} // CalculateAgeSamples

// ----------------------------------------------------------------------
public void PrintAge( DateTime birthDate, DateTime moment )
{
  Console.WriteLine( "Birthdate={0:d}, Age at {1:d} is {2} years", birthDate, moment, YearDiff( birthDate, moment ) );
} // PrintAge

简单易懂的解决方案。

// Save today's date.
var today = DateTime.Today;

// Calculate the age.
var age = today.Year - birthdate.Year;

// Go back to the year in which the person was born in case of a leap year
if (birthdate.Date > today.AddYears(-age)) age--;

然而，这假设你在寻找西方的时代观念，而不是使用东亚的推算法。

另一个功能，不是我做的，而是在网上找到的，并做了一些改进：

public static int GetAge(DateTime birthDate)
{
    DateTime n = DateTime.Now; // To avoid a race condition around midnight
    int age = n.Year - birthDate.Year;

    if (n.Month < birthDate.Month || (n.Month == birthDate.Month && n.Day < birthDate.Day))
        age--;

    return age;
}

我只想到了两件事：来自不使用公历的国家的人呢？DateTime。我认为现在是服务器特定的文化。我对实际使用亚洲日历一无所知，我不知道是否有一种简单的方法来转换日历之间的日期，但以防万一，你想知道4660年的中国人：-）

通过较少的转换和UtcNow，这段代码可以照顾闰年2月29日出生的人：

public int GetAge(DateTime DateOfBirth)
{
    var Now = DateTime.UtcNow;
    return Now.Year - DateOfBirth.Year -
        (
            (
                Now.Month > DateOfBirth.Month ||
                (Now.Month == DateOfBirth.Month && Now.Day >= DateOfBirth.Day)
            ) ? 0 : 1
        );
}