Code
<script language="JavaScript">
d0 = new Date('December 1, 2008');
d1 = new Date();
dt = (d1.getTime() - d0.getTime()) / (1000*60*60*24);
document.write('<big><font color="#008000">Возраст сайта - <font color="#FF0000">' + Math.round(dt) + ' <font color="#008000">дней</font></big>');
</script>