PHP: How to make "Birthday"

So in my community I really want a birthday in the profiles, but I don't know how to do it.

What I want to do is in the profiles theirs e.g "16" years old" if he chose in his settings: 1994-01-01, so like it counts out how old he is from the birthday he pickd in his settings.

How should i do this? I started out with 3 select´s, days, months & years.

                    <select name="days" id="days">
    <option selected="selected" value="1">1</option>
    <option value="2">2</option>
    <option value="3">3</option>
    <option value="4">4</option>
    <option value="5">5</option>
    <option value="6">6</option>
    <option value="7">7</option>

    <option value="8">8</option>
    <option value="9">9</option>
    <option value="10">10</option>
    <option value="11">11</option>
    <option value="12">12</option>
    <option value="13">13</option>

    <option value="14">14</option>
    <option value="15">15</option>
    <option value="16">16</option>
    <option value="17">17</option>
    <option value="18">18</option>
    <option value="19">19</option>

    <option value="20">20</option>
    <option value="21">21</option>
    <option value="22">22</option>
    <option value="23">23</option>
    <option value="24">24</option>
    <option value="25">25</option>

    <option value="26">26</option>
    <option value="27">27</option>
    <o开发者_如何学运维ption value="28">28</option>
    <option value="29">29</option>
    <option value="30">30</option>
    <option value="31">31</option>

</select>
<select name="months" id="months" style="width:100px;">
    <option selected="selected" value="1">januar</option>
    <option value="2">februar</option>
    <option value="3">marts</option>
    <option value="4">april</option>
    <option value="5">maj</option>

    <option value="6">juni</option>
    <option value="7">juli</option>
    <option value="8">august</option>
    <option value="9">september</option>
    <option value="10">oktober</option>
    <option value="11">november</option>

    <option value="12">december</option>

</select>
<select name="years" id="years">
    <option selected="selected" value="1950">1950</option>
    <option value="1951">1951</option>
    <option value="1952">1952</option>
    <option value="1953">1953</option>

    <option value="1954">1954</option>
    <option value="1955">1955</option>
    <option value="1956">1956</option>
    <option value="1957">1957</option>
    <option value="1958">1958</option>
    <option value="1959">1959</option>

    <option value="1960">1960</option>
    <option value="1961">1961</option>
    <option value="1962">1962</option>
    <option value="1963">1963</option>
    <option value="1964">1964</option>
    <option value="1965">1965</option>

    <option value="1966">1966</option>
    <option value="1967">1967</option>
    <option value="1968">1968</option>
    <option value="1969">1969</option>
    <option value="1970">1970</option>
    <option value="1971">1971</option>

    <option value="1972">1972</option>
    <option value="1973">1973</option>
    <option value="1974">1974</option>
    <option value="1975">1975</option>
    <option value="1976">1976</option>
    <option value="1977">1977</option>

    <option value="1978">1978</option>
    <option value="1979">1979</option>
    <option value="1980">1980</option>
    <option value="1981">1981</option>
    <option value="1982">1982</option>
    <option value="1983">1983</option>

    <option value="1984">1984</option>
    <option value="1985">1985</option>
    <option value="1986">1986</option>
    <option value="1987">1987</option>
    <option value="1988">1988</option>
    <option value="1989">1989</option>

    <option value="1990">1990</option>
    <option value="1991">1991</option>
    <option value="1992">1992</option>
    <option value="1993">1993</option>
    <option value="1994">1994</option>
    <option value="1995">1995</option>

</select>

What should i do know? How should i store them in the "birthday" field just like this: days/months/years? Is there a specific way to do this, so you can count the age later? How do you count the age..

Thank you!

If you want to calculate an age given you have when they were born, you can simply do (PHP 5.3+):

$birth = new DateTime("1986-12-02");
$now = new DateTime();
$age = $now->diff($birth)->format("%y");
echo $age; //23

Here is a solution that works with php versions below 5.3 (most hosts still use versions below):

<?php
list($year, $month, $day) = explode('-', $date);

$year = date('Y') - $year;
$month = date('m') - $month;
$day = date('d') - $day;

if ($month < 0 || ($month == 0 && $day < 0)) // Have we had a birth this year?
    $year--;

echo 'Age is ' . $year;

This requires the format to be yyyy-mm-dd. However, this is easily changed with the use of strtotime if anyone wants.