getSpecificDateTimeByPHP

<?php
	$time1 = "2015-10-03 12:02:11";
	$time2 = date('Y-m-d H:i:s',strtotime("$time1 -2 year"));
	echo $time2."<br>";//"2013-10-03 12:02:11"
	
	$time3 = '2015';
	$time4 = date('Y',strtotime("$time3 -3 year"));
	echo $time4."<br>";//"2012"
	
	$time5 = '2015-01-01';
	$time6 = date('Y',strtotime("$time4 -2 year"));
	echo $time6."<br>";//"2013"
	
	$time7 = '2015';
	$time8 = date('Y',strtotime("-1 year",time($time7)));
	echo $time8."<br>";//"2014"
	
	$time9 = '2015-01-01';
	$time10 = date('Y',strtotime("$time9 -10 year"));
	echo $time10."<br>";//"2005"
	
	$time10 = '2014-01-01';
	$time11 = date('Y',strtotime("$time10 -20 year"));
	echo $time11."<br>";//"1994"
	
	/*
	 * $time9 is much better than $time7.
	 *
	 */

Note:
The "Year (and just the year)" format only works if a time string has already been found -- otherwise this format is recognised as HH MM.
http://php.net/manual/en/datetime.formats.date.php