Insert a date value with PHP in MySQL

I would like to introduce information from a form with your date of birth through PHP to MySQL. The problem is that no matter how hard I try it in the DB, we introduce the 0000-00-00 value. If I write the date directly in the Insert there is no problem, the problem appears when I try to pass the variables that contain that information.

if (isset ($ _ GET["name"])) {

    $ name = $ _ GET['name'];
    $ lastName = $ _ GET['lastName'];
    $ age = $ _ GET['age'];
    $ dd = $ _ GET['dd'];
    $ mm = $ _ GET['mm'];
    $ yyyy = $ _ GET['yyyy'];



    $ connection = mysqli_connect ($ hostname, $ username, $ password, $ database);

    // INSERT INTO Patient (Patient_Name, Patient_LastName, Patient_Age, Patient_DOB) VALUES ("Pablo", "Mendosa", 23, "2000-12-1");


    $ query = "Insert into Patient (Patient_Name, Patient_LastName, Patient_Age, Patient_DOB) values ​​('{$ name}', '{$ lastName}', '{$ age}', '{$ yyyy}' - '{$ mm } '-' {$ dd} ') ";

    $ result = mysqli_query ($ connection, $ query);

Thank you in advance and greetings