如何利用php实现下拉框选择日期功能

<select name="year">
    <option value="2021">2021</option>
    <option value="2022">2022</option>
    <option value="2023">2023</option>
</select>

<select name="year">
    <?php
        for ($i = date("Y"); $i >= 2000; $i--) {
            echo "<option value=\"{$i}\">{$i}</option>";
        }
    ?>
</select>

<select name="year" onchange="updateMonth(this.value)">
    <?php
        for ($i = date("Y"); $i >= 2000; $i--) {
            echo "<option value=\"{$i}\">{$i}</option>";
        }
    ?>
</select>
<select name="month"></select>

function updateMonth(year) {
    var monthSelect = document.getElementsByName("month")[0];
    monthSelect.innerHTML = "";
    for (var i = 1; i <= 12; i++) {
        var option = document.createElement("option");
        option.value = i;
        option.innerHTML = i;
        monthSelect.appendChild(option);
    }
}