<?php
$ages = 22;
 
if ($ages >= 70) {
    echo "You're old";
}
elseif ($ages >= 21 && 70 > $ages) { //пропустит если будет ($ages >= 21 && 70 < $ages)
    echo "You're adult! <br>";
}
elseif ($ages < 21 && $ages >= 3) {
    echo "You're young <br>";
}
else {
    echo "You're kid <br>";
}
?>