PHP checkdate() with multiple conditions

I am trying to use checkdate() in an IF statement with other conditions:

if ( $segment[1] == 'living-life-lab' && 
     $segment[2] == 'activities' && 
     $segment[3] == 'letter-scramble-game' && 
    ( checkdate( $segment[5] , $segment[6] , $segment[4] ) === true ) ) 
{

But checkdate() returns a warning instead of just moving to the next IF when the value of $segment[4] is "printables" , $segment[5] is "rss" and $segment[6] is "feed".

Warning: checkdate() expects parameter 1 to be integer, string given in /home/vhosts/rons-home.net/LivingLifeLab/url/url.php on line 709

What change do I need to make to the IF statement to allow a date but move to the next IF when $segment[4] , $segment[5] & $segment[6] do not form a date?