人们可以这样计算“年龄”（即“西方人”的方式）：

public static int AgeInYears(this System.DateTime source, System.DateTime target)
  => target.Year - source.Year is int age && age > 0 && source.AddYears(age) > target ? age - 1 : age < 0 && source.AddYears(age) < target ? age + 1 : age;

如果时间方向为“负”，则年龄也将为负。

可以添加一个分数，代表从目标到下一个生日的累计年龄：

public static double AgeInTotalYears(this System.DateTime source, System.DateTime target)
{
  var sign = (source <= target ? 1 : -1);

  var ageInYears = AgeInYears(source, target); // The method above.

  var last = source.AddYears(ageInYears);
  var next = source.AddYears(ageInYears + sign);

  var fractionalAge = (double)(target - last).Ticks / (double)(next - last).Ticks * sign;

  return ageInYears + fractionalAge;
}

分数是过去的时间（从上一个生日到下一个生日）与总时间的比率。

无论是向前还是向后，这两种方法都以相同的方式工作。

我在这个问题上使用了以下内容。我知道它不太优雅，但它很管用。

DateTime zeroTime = new DateTime(1, 1, 1);
var date1 = new DateTime(1983, 03, 04);
var date2 = DateTime.Now;
var dif = date2 - date1;
int years = (zeroTime + dif).Year - 1;
Log.DebugFormat("Years -->{0}", years);

public string GetAge(this DateTime birthdate, string ageStrinFormat = null)
{
    var date = DateTime.Now.AddMonths(-birthdate.Month).AddDays(-birthdate.Day);
    return string.Format(ageStrinFormat ?? "{0}/{1}/{2}",
        (date.Year - birthdate.Year), date.Month, date.Day);
}

我的建议

int age = (int) ((DateTime.Now - bday).TotalDays/365.242199);

这一年似乎在正确的日期发生了变化。（我在107岁之前进行了现场测试。）

这里有一个非常简单且易于遵循的示例。

private int CalculateAge()
{
//get birthdate
   DateTime dtBirth = Convert.ToDateTime(BirthDatePicker.Value);
   int byear = dtBirth.Year;
   int bmonth = dtBirth.Month;
   int bday = dtBirth.Day;
   DateTime dtToday = DateTime.Now;
   int tYear = dtToday.Year;
   int tmonth = dtToday.Month;
   int tday = dtToday.Day;
   int age = tYear - byear;
   if (bmonth < tmonth)
       age--;
   else if (bmonth == tmonth && bday>tday)
   {
       age--;
   }
return age;
}

这为这个问题提供了“更多细节”。也许这就是你要找的

DateTime birth = new DateTime(1974, 8, 29);
DateTime today = DateTime.Now;
TimeSpan span = today - birth;
DateTime age = DateTime.MinValue + span;

// Make adjustment due to MinValue equalling 1/1/1
int years = age.Year - 1;
int months = age.Month - 1;
int days = age.Day - 1;

// Print out not only how many years old they are but give months and days as well
Console.Write("{0} years, {1} months, {2} days", years, months, days);