My object in javascript not returning the wanted value

I can’t seem to figure out how to do the object part, I need to make it calculate the age dynamically. I’ve written most of the stuff here and it works fine the only down side is my dynamic age calculation, I don’t know what I’m doing wrong and can’t find my mistake.

<html>
    <head>
        <title>WEB PROGRAMIRANJE</title>
    </head>
    <body>
        <script type="text/javascript">
        var niza=new Array (9,8,7,6,5,4,3,2,1);
        var izbrisani=niza.shift();
        var izbrisanip=niza.pop();
        var sortirani=niza.sort();
       // form an arrey delete first and last:
       // sort the arrey:
        document.write(sortirani);  

        function babati(a,b,c)
        {
            var total;
            total=(a+b+c)/3;
            alert(total);
        }
        document.write("<br>");
        </script>
                <input type="button" value="Call" onClick="babati(0,5,10)";>
                <script type="text/javascript">
                document.write("<br>");
                var ucenik=new Object();
        // giving them value to object elements:
        ucenik.ime="Name";
        ucenik.prezime="Surname";
        ucenik.godina=2021;
        ucenik.roden=2003;
        // printing the object elements:
        document.write(ucenik.ime);
        document.write("<br>");
        document.write(ucenik.prezime);
        document.write("<br>");
        document.write(ucenik.roden);
        document.write("<br>");
        // The function:
        // This will calculate the age dinamicly This year - Birth year:
        ucenik.vozrast=function()
        {
            this.godina - this.roden;   
        }
        ucenik.vozrast();
        document.write(ucenik.vozrast);
         //This line above prints the dynamic age:
        </script>
    </body>
</html>