<form action="index.php" method="get">
<script>
    for (var a=0; a<61; a++){
        document.getElementById("content").innerHTML = '<input type="checkbox" name="cyfra"> '+ a +'<br>';
    }
<div id="content"</div>
    </script>
</p>
<input type="submit" value="Wyswietl" />
</form>

<?php

$l1 = $_GET['cyfra'];
$l2 = $_GET['cyfra'];
$l3 = $_GET['cyfra'];
$l4 = $_GET['cyfra'];
$l5 = $_GET['cyfra'];
$l6 = $_GET['cyfra'];
if($_GET['cyfra']< 7){
echo $l1 ," ", $l2 ," ", $l3 ," ", $l4 ," ", $l5 ," ", $l6 ," ";
}
else{
    echo "za duzo znaków";
}
?>