var date = new Date();
    var year= date.getFullYear();
    var month= date.getMonth();
    month= month + 1;
    var date= date.getDate();

var birthyear = 1980;
var birthmonth = 2;
var birthday = 21;

var age = 0;
if ((month>birthmonth) || ((month==birthmonth) && (date>=birthday))) {
   age = year - birthyear;
}
else {
   age = year - birthyear - 1;
}
//document.write("Today's Date:" + month + "/" + date + "/" + year);

//document.write("<BR>Birthdate: " + birthmonth + "/" + birthday + "/" + birthyear);

//document.write("<BR>Age: ");

document.write(age);