Add 21 days to the date picker on a gravity form. This is useful for only allowing people to select a date in the future.

footer.php

<?php
###########################
//added by [email protected] on 29/4/2019
//if this is the marketing form (form id:14) then activate some 
//script so user cannot select any date earlier than 21 days.
###########################
if(is_single(251)){ 
?>
	<script>
		jQuery(document).ready(function($) {
			$(".datepicker").datepicker({ 
				minDate: 21,
				dateFormat: 'dd/mm/yy', 
				//maxDate:'0',
				showOn: "button",
				buttonImage: "http://jqueryui.com/resources/demos/datepicker/images/calendar.gif",
				buttonImageOnly: true 
			});		
		});
	</script>
<?php } 
###########################
?>