date() method, “A non well formed numeric value encountered” does not want to format a date passed in $_POST

From the documentation for strtotime():

Dates in the m/d/y or d-m-y formats are disambiguated by looking at the separator between the various components: if the separator is a slash (/), then the American m/d/y is assumed; whereas if the separator is a dash (-) or a dot (.), then the European d-m-y format is assumed.

In your date string, you have 12-16-2013. 16 isn't a valid month, and hence strtotime() returns false.

Since you can't use DateTime class, you could manually replace the - with / using str_replace() to convert the date string into a format that strtotime() understands:

$date = '2-16-2013';
echo date('Y-m-d', strtotime(str_replace('-','/', $date))); // => 2013-02-16

You need to understand over here the date format of your date. Here m/d/Y is considered to be the standard American Date format.

So when your date is like

'09/06/2014',//it should be considered as 06 september 2014
'04/07/2014',//it should be considered as 07 april 2014

And when your date is like as

'21/05/2014',
'22/05/2014',

Then the above date doesn't fits within the standards of American Date Format i.e. m/d/Y instead what you can do over here is replace / along with - which converts your date into European Date Format which is d-m-Y

This means that the second parameter for date() is expecting integer, so convert $row['posted'] to timestamp first.

Try

$posted = date('d/m/Y H:i:s', strtotime($row['posted']));