Variables and IF/ELSE statements

I am trying to build an app that will alert users full name and age category from young, average, and old age but no matter which age i type in it says "You belong to young category". Please tell me what is wrong with my code. Here it is:

<script type="text/javascript"> 
    var godine = 25;
    var starost;
    if (godine < 30) {
        starost = " Vi pripadate u kategoriju mladih.";
    }
    if ((godine >= 30) && (godine < 70)) {
        starost = " Vi pripadate u kategoriju srednje starih.";
    }
    if (godine > 70) {
        starost = " Vi pripadate u kategoriju starih";
    }

    </script>
    <h1>Dobro dosli na kategorisanje starosti</h1>
    <form action="" name="frmLogin" onsubmit="alert('Korisnice: ' + ' ' + document.frmLogin.txtIme.value + ' ' + document.frmLogin.txtPrezime.value + document.frmLogin.txtStarost.value + starost)">
        Korisnicko ime: <input type="text" name="txtIme"/>
        <br>
        Korisnicko prezime: <input type="text" name="txtPrezime">
        <br>
        Godine: <input type="text" name="txtStarost">
        <br>
        <input type="submit" value="Pokreni program">
    </form>