var today = new Date();
var birth = new Date(1981, 1, 4, 0, 0, 0);
var age = today.getFullYear() - birth.getFullYear();
var newAge = 0;

if (today.getMonth() < birth.getMonth())
{
	newAge = age - 1;
}
else
{
	if (today.getMonth() > birth.getMonth())
	{
		newAge = age;
	}
	else
	{
		if (today.getDate() < birth.getDate())
		{
			newAge = age - 1;
		}
		else
		{
			newAge = age;
		}
	}
}
document.write(newAge);