JavaScript Age Calculation

function IsValidAge(agelimit) {

var month = document.getElementById("ddlMonth").selectedIndex-1;

var day = $("#ddlDay option:selected").val();

var year = $("#ddlYear option:selected").val();

var Birthdate = new Date(year, month, day);

var Today = new Date();

var diff = new Date(Today - Birthdate);

var days = diff / 1000 / 60 / 60 / 24 / 365.25;

var age = Math.round(days);

return age > agelimit ? true : false;

}