我对DateTime一无所知，但我能做的就是：

using System;
                    
public class Program
{
    public static int getAge(int month, int day, int year) {
        DateTime today = DateTime.Today;
        int currentDay = today.Day;
        int currentYear = today.Year;
        int currentMonth = today.Month;
        int age = 0;
        if (currentMonth < month) {
            age -= 1;
        } else if (currentMonth == month) {
            if (currentDay < day) {
                age -= 1;
            }
        }
        currentYear -= year;
        age += currentYear;
        return age;
    }
    public static void Main()
    {
        int ageInYears = getAge(8, 10, 2007);
        Console.WriteLine(ageInYears);
    }
}

有点困惑，但仔细看代码，这一切都是有意义的。

这个经典问题值得野田时间来解决。

static int GetAge(LocalDate dateOfBirth)
{
    Instant now = SystemClock.Instance.Now;

    // The target time zone is important.
    // It should align with the *current physical location* of the person
    // you are talking about.  When the whereabouts of that person are unknown,
    // then you use the time zone of the person who is *asking* for the age.
    // The time zone of birth is irrelevant!

    DateTimeZone zone = DateTimeZoneProviders.Tzdb["America/New_York"];

    LocalDate today = now.InZone(zone).Date;

    Period period = Period.Between(dateOfBirth, today, PeriodUnits.Years);

    return (int) period.Years;
}

用法：

LocalDate dateOfBirth = new LocalDate(1976, 8, 27);
int age = GetAge(dateOfBirth);

您可能还对以下改进感兴趣：

将时钟作为IClock传递，而不是使用SystemClock.Instance，将提高可测试性。目标时区可能会更改，因此您也需要DateTimeZone参数。

另请参阅我关于这个主题的博客文章：处理生日和其他周年纪念日

这是最准确的答案之一，它能够解决2月29日的生日，而不是2月28日的任何一年。

public int GetAge(DateTime birthDate)
{
    int age = DateTime.Now.Year - birthDate.Year;

    if (birthDate.DayOfYear > DateTime.Now.DayOfYear)
        age--;

    return age;
}

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。

var startDate = new DateTime(2015, 04, 05);//your start date
var endDate = DateTime.Now;
var years = 0;
while(startDate < endDate) 
{
     startDate = startDate.AddYears(1);
     if(startDate < endDate) 
     {
         years++;
     }
}

以下是使用DateTimeOffset和手动数学的答案：

var diff = DateTimeOffset.Now - dateOfBirth;
var sinceEpoch = DateTimeOffset.UnixEpoch + diff;

return sinceEpoch.Year - 1970;