we can give the functionality of age finder in our web application using JavaScript.

Java script

<SCRIPT LANGUAGE="JavaScript">

var mm = prompt('What month were you born in?','1-12');

var bday = prompt('What day were you born on?','1-31');

var byear = prompt('What year were you born in?','1975');

var year = new Date();

var year2 = year.getYear();

var year3 = (year < 2000) ? year2 + 1900 : year2;

thedate = new Date();

mm2 = thedate.getMonth() + 1;

dd2 = thedate.getDate();

yy2 = thedate.getYear();

if (yy2 < 100) yy2 += 1900

yourage = yy2 - byear;

if (mm2 < mm) yourage--;

if ((mm2 == mm) && (dd2 < bday)) yourage--;

TMonth = new Array(

'January','February','March',

'April','May','June','July',

'August','September','October',

'November','December'

);

CurMonth = mm - 1;

bmonth = TMonth[CurMonth];

var age2 = yourage + 1;

var timerID;

var timerRunning = false;

var today = new Date();

var startday = new Date();

var enday = new Date();

var secPerDay = 0;

var minPerDay = 0;

var hourPerDay = 0;

var secsLeft = 0;

var secsRound = 0;

var secsRemain = 0;

var minLeft = 0;

var minRound = 0;

var minRemain = 0;

var timeRemain = 0;

function stopclock() {

if(timerRunning)

clearTimeout(timerID);

timerRunning = false;

}

function startclock() {

stopclock();

showtime();

showtime1();

}

function showtime() {

today = new Date();

enday = new Date(""+bmonth+", "+bday+" "+year3+" 00:00");

enday.setYear(""+year3+"");

secsPerDay = 1000 ;

minPerDay = 60 * 1000 ;

hoursPerDay = 60 * 60 * 1000;

PerDay = 24 * 60 * 60 * 1000;

secsLeft = (enday.getTime() - today.getTime()) / minPerDay;

secsRound = Math.round(secsLeft);

secsRemain = secsLeft - secsRound;

secsRemain = (secsRemain < 0) ? secsRemain = 60 - ((secsRound - secsLeft) * 60) : secsRemain = (secsLeft - secsRound) * 60;

secsRemain = Math.round(secsRemain);

minLeft = ((enday.getTime() - today.getTime()) / hoursPerDay);

minRound = Math.round(minLeft);

minRemain = minLeft - minRound;

minRemain = (minRemain < 0) ? minRemain = 60 - ((minRound - minLeft)  * 60) : minRemain = ((minLeft - minRound) * 60);

minRemain = Math.round(minRemain - 0.495);

hoursLeft = ((enday.getTime() - today.getTime()) / PerDay);

hoursRound = Math.round(hoursLeft);

hoursRemain = hoursLeft - hoursRound;

hoursRemain = (hoursRemain < 0) ? hoursRemain = 24 - ((hoursRound - hoursLeft)  * 24) : hoursRemain = ((hoursLeft - hoursRound) * 24);

hoursRemain = Math.round(hoursRemain - 0.5);

daysLeft = ((enday.getTime() - today.getTime()) / PerDay);

daysLeft = (daysLeft - 0.5);

daysRound = Math.round(daysLeft);

daysRemain = daysRound;

if (daysRemain == 1) day_rem = " day, "

else day_rem = " days, "

if (hoursRemain == 1) hour_rem = " hour, "

else hour_rem = " hours, "

if (minRemain == 1) min_rem = " minute, "

else min_rem = " minutes, "

if (secsRemain == 1) sec_rem = " second"

else sec_rem = " seconds"

timeRemain = daysRemain + day_rem + hoursRemain + hour_rem + minRemain + min_rem + secsRemain + sec_rem;

document.down.face.value = timeRemain;

timerID = setTimeout("showtime()",1000);

timerRunning = true;

if (daysRemain < 0) year3 = year3 + 1

}

function showtime1() {

startday = new Date(""+bmonth+" "+bday+", "+byear+" 00:00 EDT");

startday.setYear(""+byear+"");

today = new Date();

secsPerDay = 1000 ;

minPerDay = 60 * 1000 ;

hoursPerDay = 60 * 60 * 1000;

PerDay = 24 * 60 * 60 * 1000;

secsLeft = (today.getTime() - startday.getTime()) / minPerDay;

secsRound = Math.round(secsLeft);

secsRemain = secsLeft - secsRound;

secsRemain = (secsRemain < 0) ? secsRemain = 60 - ((secsRound - secsLeft) * 60) : secsRemain = (secsLeft - secsRound) * 60;

secsRemain = Math.round(secsRemain);

minLeft = ((today.getTime() - startday.getTime()) / hoursPerDay);

minRound = Math.round(minLeft);

minRemain = minLeft - minRound;

minRemain = (minRemain < 0) ? minRemain = 60 - ((minRound - minLeft) * 60) : minRemain = ((minLeft - minRound) * 60);

minRemain = Math.round(minRemain - 0.495);

hoursLeft = ((today.getTime() - startday.getTime()) / PerDay);

hoursRound = Math.round(hoursLeft);

hoursRemain = hoursLeft - hoursRound;

hoursRemain = (hoursRemain < 0) ? hoursRemain = 24 - ((hoursRound - hoursLeft) * 24)  : hoursRemain = ((hoursLeft - hoursRound) * 24);
hoursRemain = Math.round(hoursRemain - 0.5);
daysLeft = ((today.getTime() - startday.getTime()) / PerDay);
daysLeft = (daysLeft - 0.5);
daysRound = Math.round(daysLeft);
daysRemain = daysRound;
if (daysRemain == 1) day_rem = " day, "
else day_rem = " days, "
if (hoursRemain == 1) hour_rem = " hour, "
else hour_rem = " hours, "
if (minRemain == 1) min_rem = " minute, "
else min_rem = " minutes, "
if (secsRemain == 1) sec_rem = " second"
else sec_rem = " seconds"
timeRemain = daysRemain + day_rem + hoursRemain + hour_rem + minRemain + min_rem + secsRemain + sec_rem;
document.up.face.value = timeRemain;
timerID = setTimeout("showtime1()",1000);
timerRunning = true;
}
</SCRIPT>
</head>

Html Design
<html>
<BODY OnLoad="startclock()" bgcolor=#009999>         
<center>
<form name="down" onSubmit="0">
<script Language="JavaScript">
document.write("<b>I was born "+bmonth+" "+bday+", "+byear+".  ("+mm+"/"+bday+"/"+byear+")</b>");
document.write("<br><br>I am "+yourage+" years old, and will turn "+age2+" in:");
</script>
<br>
<input type="text" name="face" size="47" >
</form>
<p>
<br>
<form name="up" onSubmit="1">
I've been alive for...<br>
<input type="text" name="face" size="47" >
</form>
</center>
</BODY>
</html>