jsprint fiddle

HTML

<script src="http://brigand.github.io/jsprint/build/output/jsprint.min.js"></script>
<script src="http://cdnjs.cloudflare.com/ajax/libs/moment.js/2.4.0/moment.min.js"></script>

JavaScript

function validate(date){
    var eighteenYearsAgo = moment().subtract(18, "years");
    var birthday = moment(date);
    
    if (!birthday.isValid()) {
        return "invalid date";    
    }
    else if (eighteenYearsAgo.isAfter(birthday)) {
        return "okay, you're good";    
    }
    else {
        return "sorry, no";    
    }
}

jsprint(validate, "4/10/1995");