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++;
     }
}

我经常用手指数。我需要看一下日历，以确定事情何时发生变化。这就是我在代码中要做的：

int AgeNow(DateTime birthday)
{
    return AgeAt(DateTime.Now, birthday);
}

int AgeAt(DateTime now, DateTime birthday)
{
    return AgeAt(now, birthday, CultureInfo.CurrentCulture.Calendar);
}

int AgeAt(DateTime now, DateTime birthday, Calendar calendar)
{
    // My age has increased on the morning of my
    // birthday even though I was born in the evening.
    now = now.Date;
    birthday = birthday.Date;

    var age = 0;
    if (now <= birthday) return age; // I am zero now if I am to be born tomorrow.

    while (calendar.AddYears(birthday, age + 1) <= now)
    {
        age++;
    }
    return age;
}

在LINQPad中运行此过程可获得以下结果：

PASSED: someone born on 28 February 1964 is age 4 on 28 February 1968
PASSED: someone born on 29 February 1964 is age 3 on 28 February 1968
PASSED: someone born on 31 December 2016 is age 0 on 01 January 2017

LINQPad中的代码在这里。

        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) ";

我强烈建议使用名为AgeCalculator的NuGet软件包，因为在计算年龄（闰年、时间成分等）时需要考虑很多事情，而且只有两行代码不能削减它。该库给您的时间不只是一年。它甚至在计算时考虑了时间成分，这样你就可以得到一个包含年、月、日和时间成分的准确年龄。更为先进的是，可以选择将2月29日作为闰年，而将2月28日作为非闰年。

我使用这个：

public static class DateTimeExtensions
{
    public static int Age(this DateTime birthDate)
    {
        return Age(birthDate, DateTime.Now);
    }

    public static int Age(this DateTime birthDate, DateTime offsetDate)
    {
        int result=0;
        result = offsetDate.Year - birthDate.Year;

        if (offsetDate.DayOfYear < birthDate.DayOfYear)
        {
              result--;
        }

        return result;
    }
}