Get Age - JavaScript function

HTML

<h1>Age Calculator</h1>
<p><label>Day:</label><input type="date" id="day" value="16" /></p>

<p><input type="submit" id="submit" value="Calculate Age" /></p>

CSS

body {
    text-align:center;
    font-family:arial, san-serif;
    padding:20px;
}

input {
    margin:5px;
}

h1 {
    font-size:30px;
    margin:0 0 10px 0;
}
label {
    display:inline-block;
    width:60px;
    text-align:right;
}

JavaScript

function getAge(DOB) {
    var today = new Date();
    var birthDate = new Date(DOB);
    var age = today.getFullYear() - birthDate.getFullYear();
    var m = today.getMonth() - birthDate.getMonth();
    if (m < 0 || (m === 0 && today.getDate() < birthDate.getDate())) {
        age = age - 1;
    }

    return age;
}

(function( jQuery ){
    
    $('#submit').click(function(){
        var birth_date = $('#month').val();
        alert( getAge( birth_date ) );
    });
    
})($)