рони,
Без обид, но выкинь свой говнокод
за 10 мин наваял
var day = 24;
var month = 8;
var year = 1990;
var now = new Date().getTime();
var birsday = Date.UTC(year,month-1,day);
var result = new Date();
result.setTime(now-birsday);
alert(result.getFullYear() - 1970)
alert(result.getMonth())
alert(result.getDay())