Iam trying to find the retirement date from joining date at the age of 58 years in php : Iam trying to find the retirement date from joining date at the age of 58 years in php.

        $retire_date = date('Y-m-d', strtotime($joining_date. '+58 years'));  
        
it's showing 1970-01-01 , Up to "+40 years" it's showing correctly.can anyone contribute to find this one  