JS Adding Methods

<html>
<head>
<script type="text/javascript">

	function people(name, age) {
		this.name = name;
		this.age = age;
		this.yearsUntilRetrite = yearsLeft;
		}

	function yearsLeft() {
		var numYears = 65 - this.age;
		return numYears;
	}

	var natalie = new people("Natalie Portman",28)
	var bucky = new people("Bucky Robers",24)

	function ludzie(imie, lata){
		this.imie = imie;
		this.lata = lata;
	}

	var jan = new ludzie("Jan Kowalski",15)
	var mietek = new ludzie("Mietek Miś",23)

</script>
</head>
<body>
<script type="text/javascript">

document.writeln(bucky.yearsUntilRetrite());
document.writeln(mietek.imie)
</script>
</body>
</html>