form_date_class Invalid date input

I am attempting to ask for the user to pick their date of birth and then validate they are not older than 123 years and not younger than 18 years.

Here is my time code
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$today = date("Y-m-d");
$timestamp = strtotime($today);
$m = date('m',$timestamp);
$d = date('d',$timestamp);
$Y = date('Y',$timestamp);
$oldest_date = mktime(0,0,0,$m,$d,($Y-123));
$youngest_date = mktime(0,0,0,$m,$d,($Y-18));
-------------------------

And here is my AddInput
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$form->AddInput(array(
"TYPE"=>"custom",
"ID"=>"dob",
"LABEL"=>"Your <u>B</u>irth Date",
"ACCESSKEY"=>"B",
"CustomClass"=>"form_date_class",
"VALUE"=>$today,
"Format"=>"{month} month / {day} day / {year} year",
"Months"=>array(
"01"=>"January",
"02"=>"February",
"03"=>"March",
"04"=>"April",
"05"=>"May",
"06"=>"June",
"07"=>"July",
"08"=>"August",
"09"=>"September",
"10"=>"October",
"11"=>"November",
"12"=>"December"
),
"ValidationStartDate"=>$oldest_date,
"ValidationStartDateErrorMessage"=>"You cannot be older than the oldest person on record.",
"ValidationEndDate"=>$youngest_date,
"ValidationEndDateErrorMessage"=>"You must be 18 years of age or older to apply.",
));
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Either the VALUE, ValidationStartDate and ValidationEndDate must be in the YYYY-MM-DD format, like for instance '2010-01-30'.

Thank you very much, I am sure this information was somewhere in the documentation!