function getAge(dateString) {

    var today = new Date();

    var birthDate = new Date(dateString);

    var age = today.getFullYear() - birthDate.getFullYear();

    var m = today.getMonth() - birthDate.getMonth();

    if (m < 0 || (m === 0 && today.getDate() < birthDate.getDate())) {

        age--;

    }

    return age > 18;

}

console.log(getAge('1997-11-09'))