MSDN帮助为什么没有告诉您这一点？看起来很明显：

System.DateTime birthTime = AskTheUser(myUser); // :-)
System.DateTime now = System.DateTime.Now;
System.TimeSpan age = now - birthTime; // As simple as that
double ageInDays = age.TotalDays; // Will you convert to whatever you want yourself?

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。

这是一个非常简单的方法：

int Age = DateTime.Today.Year - new DateTime(2000, 1, 1).Year;

这是一个非常适合我的功能。没有计算，非常简单。

    public static string ToAge(this DateTime dob, DateTime? toDate = null)
    {
        if (!toDate.HasValue)
            toDate = DateTime.Now;
        var now = toDate.Value;

        if (now.CompareTo(dob) < 0)
            return "Future date";

        int years = now.Year - dob.Year;
        int months = now.Month - dob.Month;
        int days = now.Day - dob.Day;

        if (days < 0)
        {
            months--;
            days = DateTime.DaysInMonth(dob.Year, dob.Month) - dob.Day + now.Day;
        }

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


        return string.Format("{0} year(s), {1} month(s), {2} days(s)",
            years,
            months,
            days);
    }

这里是一个单元测试：

    [Test]
    public void ToAgeTests()
    {
        var date = new DateTime(2000, 1, 1);
        Assert.AreEqual("0 year(s), 0 month(s), 1 days(s)", new DateTime(1999, 12, 31).ToAge(date));
        Assert.AreEqual("0 year(s), 0 month(s), 0 days(s)", new DateTime(2000, 1, 1).ToAge(date));
        Assert.AreEqual("1 year(s), 0 month(s), 0 days(s)", new DateTime(1999, 1, 1).ToAge(date));
        Assert.AreEqual("0 year(s), 11 month(s), 0 days(s)", new DateTime(1999, 2, 1).ToAge(date));
        Assert.AreEqual("0 year(s), 10 month(s), 25 days(s)", new DateTime(1999, 2, 4).ToAge(date));
        Assert.AreEqual("0 year(s), 10 month(s), 1 days(s)", new DateTime(1999, 2, 28).ToAge(date));

        date = new DateTime(2000, 2, 15);
        Assert.AreEqual("0 year(s), 0 month(s), 28 days(s)", new DateTime(2000, 1, 18).ToAge(date));
    }

只需使用：

(DateTime.Now - myDate).TotalHours / 8766.0

当前日期-myDate=TimeSpan，获取总小时数并除以每年的总小时数，得到确切的年龄/月/日。。。

==常见说法（从几个月到几岁）===

如果您只是为了通用，以下是代码作为您的信息：

DateTime today = DateTime.Today;
DateTime bday = DateTime.Parse("2016-2-14");
int age = today.Year - bday.Year;
var unit = "";

if (bday > today.AddYears(-age))
{
    age--;
}
if (age == 0)   // Under one year old
{
    age = today.Month - bday.Month;

    age = age <= 0 ? (12 + age) : age;  // The next year before birthday

    age = today.Day - bday.Day >= 0 ? age : --age;  // Before the birthday.day

    unit = "month";
}
else {
    unit = "year";
}

if (age > 1)
{
    unit = unit + "s";
}

测试结果如下：

The birthday: 2016-2-14

2016-2-15 =>  age=0, unit=month;
2016-5-13 =>  age=2, unit=months;
2016-5-14 =>  age=3, unit=months; 
2016-6-13 =>  age=3, unit=months; 
2016-6-15 =>  age=4, unit=months; 
2017-1-13 =>  age=10, unit=months; 
2017-1-14 =>  age=11, unit=months; 
2017-2-13 =>  age=11, unit=months; 
2017-2-14 =>  age=1, unit=year; 
2017-2-15 =>  age=1, unit=year; 
2017-3-13 =>  age=1, unit=year;
2018-1-13 =>  age=1, unit=year; 
2018-1-14 =>  age=1, unit=year; 
2018-2-13 =>  age=1, unit=year; 
2018-2-14 =>  age=2, unit=years;