Returns the number years, months, days and minutes that have elapsed since a given date. Designed for displaying my daughters age on her web site.

getage.js

var MILLIS_DAY = 24 * 60 * 60 * 1000;
var MILLIS_HOUR = 60 * 60 * 1000;
var MILLIS_MINUTE = 60 * 1000;
var MILLIS_MONTH = 30 * 24 * 60 * 60 * 1000;
var MILLIS_YEAR = 31557600000;

function getAge( birthday )
{
  var days = null;
	var difference = null;
	var minutes = null;
	var months = null;
	var result = null;
	var today = null;
	var years = null;
	
	result = 'I am ';
	
	today = new Date();
	difference = today.getTime() - birthday.getTime();
	
	years = Math.floor( difference / MILLIS_YEAR );
	difference = difference - ( years * MILLIS_YEAR );
	
	if( years == 1 )
	{
		result = result + years + ' year, ';
	} else {
		result = result + years + ' years, ';		
	}
	
	months = Math.floor( difference / MILLIS_MONTH );
	difference = difference - ( months * MILLIS_MONTH );
	
	if( months == 1 )
	{
		result = result + months + ' month, ';
	} else {
		result = result + months + ' months, ';		
	}	
	
	days = Math.floor( difference / MILLIS_DAY );
	difference = difference - ( days * MILLIS_DAY );
	
	if( days == 1 )
	{
		result = result + days + ' day, ';
	} else {
		result = result + days + ' days, ';		
	}	
	
	hours = Math.floor( difference / MILLIS_HOUR );
	difference = difference - ( hours * MILLIS_HOUR );
	
	if( hours == 1 )
	{
		result = result + hours + ' hour, ';
	} else {
		result = result + hours + ' hours, ';		
	}	
	
	minutes = Math.floor( difference / MILLIS_MINUTE );	

	if( minutes == 1 )
	{
		result = result + ' and ' + minutes + ' minute old.';
	} else {
		result = result + ' and ' + minutes + ' minutes old.';		
	}
	
	return result;
}

document.writeln( getAge( new Date( 2004, 5, 4, 0, 58 ) ) );