我检查了之前展示的例子，它们并不是在所有情况下都有效，因此我自己写了一个脚本。我测试过了，效果很好。

function getAge(birth) {
   var today = new Date();
   var curr_date = today.getDate();
   var curr_month = today.getMonth() + 1;
   var curr_year = today.getFullYear();

   var pieces = birth.split('/');
   var birth_date = pieces[0];
   var birth_month = pieces[1];
   var birth_year = pieces[2];

   if (curr_month == birth_month && curr_date >= birth_date) return parseInt(curr_year-birth_year);
   if (curr_month == birth_month && curr_date < birth_date) return parseInt(curr_year-birth_year-1);
   if (curr_month > birth_month) return parseInt(curr_year-birth_year);
   if (curr_month < birth_month) return parseInt(curr_year-birth_year-1);
}

var age = getAge('18/01/2011');
alert(age);

function getAge(dateString) {

    var dates = dateString.split("-");
    var d = new Date();

    var userday = dates[0];
    var usermonth = dates[1];
    var useryear = dates[2];

    var curday = d.getDate();
    var curmonth = d.getMonth()+1;
    var curyear = d.getFullYear();

    var age = curyear - useryear;

    if((curmonth < usermonth) || ( (curmonth == usermonth) && curday < userday   )){

        age--;

    }

    return age;
}

获取欧洲日期输入时的年龄:

getAge('16-03-1989')

使用ES6的干净的一行程序解决方案:

const getAge = birthDate => Math.floor((new Date() - new Date(birthDate).getTime()) / 3.15576e+10)

// today is 2018-06-13
getAge('1994-06-14') // 23
getAge('1994-06-13') // 24

我使用的是365.25天的一年(因为闰年是0.25天)，分别是3.15576e+10毫秒(365.25 * 24 * 60 * 60 * 1000)。

它有几个小时的剩余时间，所以根据用例，它可能不是最佳选择。

function age()
{
    var birthdate = $j('#birthDate').val(); // in   "mm/dd/yyyy" format
    var senddate = $j('#expireDate').val(); // in   "mm/dd/yyyy" format
    var x = birthdate.split("/");    
    var y = senddate.split("/");
    var bdays = x[1];
    var bmonths = x[0];
    var byear = x[2];
    //alert(bdays);
    var sdays = y[1];
    var smonths = y[0];
    var syear = y[2];
    //alert(sdays);

    if(sdays < bdays)
    {
        sdays = parseInt(sdays) + 30;
        smonths = parseInt(smonths) - 1;
        //alert(sdays);
        var fdays = sdays - bdays;
        //alert(fdays);
    }
    else{
        var fdays = sdays - bdays;
    }

    if(smonths < bmonths)
    {
        smonths = parseInt(smonths) + 12;
        syear = syear - 1;
        var fmonths = smonths - bmonths;
    }
    else
    {
        var fmonths = smonths - bmonths;
    }

    var fyear = syear - byear;
    document.getElementById('patientAge').value = fyear+' years '+fmonths+' months '+fdays+' days';
}

如果你需要以月为单位的年龄(天是近似值):

birthDay=28;
birthMonth=7;
birthYear=1974;

var  today = new Date();
currentDay=today.getUTCDate();
currentMonth=today.getUTCMonth() + 1;
currentYear=today.getFullYear();

//calculate the age in months:
Age = (currentYear-birthYear)*12 + (currentMonth-birthMonth) + (currentDay-birthDay)/30;

试试这个:

$('#Datepicker').change(function(){

var $bef = $('#Datepicker').val();
var $today = new Date();
var $before = new Date($bef);
var $befores = $before.getFullYear();
var $todays = $today.getFullYear();
var $bmonth = $before.getMonth();
var $tmonth = $today.getMonth();
var $bday = $before.getDate();
var $tday = $today.getDate();

if ($bmonth>$tmonth)
{$('#age').val($todays-$befores);}

if ($bmonth==$tmonth)
{   
if ($tday > $bday) {$('#age').val($todays-$befores-1);}
else if ($tday <= $bday) {$('#age').val($todays-$befores);}
}
else if ($bmonth<$tmonth)
{ $('#age').val($todays-$befores-1);} 
})