As all of us are aware, either methods are not completely foolproof.
If you just want Yes/ No, you could simply make a landing page with 2 buttons - Yes and No. Link the Yes button to the main site and No button to Google.com or some other custom page that says their access is denied as they're underage.
<?php
$msg = null;
if ((is_numeric($_POST['month']) && !empty($_POST['month'])) &&
(is_numeric($_POST['day']) && !empty($_POST['day'])) &&
(is_numeric($_POST['year']) && !empty($_POST['year']))
){
$month = $_POST['month'];
$day = $_POST['day'];
$year = $_POST['year'];
if ($year < 1994){
// redirects to new location
header('Location: http://www.google.com/');
}else{
$user_timestamp = mktime(0, 0, 0, $month, $day, $year);
$legal_timestamp = strtotime('-18 years');
if($user_timestamp < $legal_timestamp){
// redirects to new location
header('Location: http://www.yahoo.com/');
}else{
$msg = "Underage not allowed to to access content";
}
}
}
?>
<div style="float:center; margin-left:30px;">
<?php if (!empty($msg)): ?>
<div style="float:center; width:300px; color:red; border:1px solid red"><?php echo $msg; ?></div>
<?php else: ?>
<form name="myform" method="post" action="<?php echo $_SERVER['PHP_SELF']?>">
<select style="float:center; margin-right:5px;" name="month">
<option value="MM">MM</option>
<option value="01">01</option>
<option value="02">02</option>
<option value="03">03</option>
<option value="04">04</option>
<option value="05">05</option>
<option value="06">06</option>
<option value="07">07</option>
<option value="08">08</option>
<option value="09">09</option>
<option value="10">10</option>
<option value="11">11</option>
<option value="12">12</option>
</select>
<select style="float:center; margin-right:5px;" name="day">
<option value="DD">DD</option>
<option value="01">01</option>
<option value="02">02</option>
<option value="03">03</option>
<option value="04">04</option>
<option value="05">05</option>
<option value="06">06</option>
<option value="07">07</option>
<option value="08">08</option>
<option value="09">09</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>
<option value="28">28</option>
<option value="29">29</option>
<option value="30">30</option>
<option value="31">31</option>
</select>
<select style="float:center;" name="year">
<option value="YYYY">YYYY</option>
<option value="2012">2012</option>
<option value="2011">2011</option>
<option value="2010">2010</option>
<option value="2009">2009</option>
<option value="2008">2008</option>
<option value="2007">2007</option>
<option value="2006">2006</option>
<option value="2005">2005</option>
<option value="2004">2004</option>
<option value="2003">2003</option>
<option value="2002">2002</option>
<option value="2001">2001</option>
<option value="2000">2000</option>
<option value="1999">1999</option>
<option value="1998">1998</option>
<option value="1997">1997</option>
<option value="1996">1996</option>
<option value="1995">1995</option>
<option value="1994">1994</option>
<option value="1993">1993</option>
<option value="1992">1992</option>
<option value="1991">1991</option>
<option value="1990">1990</option>
<option value="1989">1989</option>
<option value="1988">1988</option>
<option value="1987">1987</option>
<option value="1986">1986</option>
<option value="1985">1985</option>
<option value="1984">1984</option>
<option value="1983">1983</option>
<option value="1982">1982</option>
<option value="1981">1981</option>
<option value="1980">1980</option>
<option value="1979">1979</option>
<option value="1978">1978</option>
<option value="1977">1977</option>
<option value="1976">1976</option>
<option value="1975">1975</option>
<option value="1974">1974</option>
<option value="1973">1973</option>
<option value="1972">1972</option>
<option value="1971">1971</option>
<option value="1970">1970</option>
<option value="1969">1969</option>
<option value="1968">1968</option>
<option value="1967">1967</option>
<option value="1966">1966</option>
<option value="1965">1965</option>
<option value="1964">1964</option>
<option value="1963">1963</option>
<option value="1962">1962</option>
<option value="1961">1961</option>
<option value="1960">1960</option>
<option value="1959">1959</option>
<option value="1958">1958</option>
<option value="1957">1957</option>
<option value="1956">1956</option>
<option value="1955">1955</option>
<option value="1954">1954</option>
<option value="1953">1953</option>
<option value="1952">1952</option>
<option value="1951">1951</option>
<option value="1950">1950</option>
<option value="1949">1949</option>
<option value="1948">1948</option>
<option value="1947">1947</option>
<option value="1946">1946</option>
<option value="1945">1945</option>
<option value="1944">1944</option>
<option value="1943">1943</option>
<option value="1942">1942</option>
<option value="1941">1941</option>
<option value="1940">1940</option>
<option value="1939">1939</option>
<option value="1938">1938</option>
<option value="1937">1937</option>
<option value="1936">1936</option>
<option value="1935">1935</option>
<option value="1934">1934</option>
<option value="1933">1933</option>
<option value="1932">1932</option>
<option value="1931">1931</option>
<option value="1930">1930</option>
<option value="1929">1929</option>
<option value="1928">1928</option>
<option value="1927">1927</option>
<option value="1926">1926</option>
<option value="1925">1925</option>
<option value="1924">1924</option>
<option value="1923">1923</option>
<option value="1922">1922</option>
<option value="1921">1921</option>
<option value="1920">1920</option>
<option value="1919">1919</option>
<option value="1918">1918</option>
<option value="1917">1917</option>
<option value="1916">1916</option>
<option value="1915">1915</option>
<option value="1914">1914</option>
<option value="1913">1913</option>
<option value="1912">1912</option>
<option value="1911">1911</option>
<option value="1910">1910</option>
<option value="1909">1909</option>
<option value="1908">1908</option>
<option value="1907">1907</option>
<option value="1906">1906</option>
<option value="1905">1905</option>
<option value="1904">1904</option>
<option value="1903">1903</option>
<option value="1902">1902</option>
<option value="1901">1901</option>
<option value="1900">1900</option>
</select>
<input type="submit" name="Submit" value="Submit" />
</form>
<?php endif; ?>
</div>
