Show the date that the user joined on their frontend profile page.

my_pmpro_member_profile_edit_user_object_fields_add_join_date.php

<?php

/**
 * Show the date that the user joined on their frontend profile page.
 * 
 * You can add this recipe to your site by creating a custom plugin
 * or using the Code Snippets plugin available for free in the WordPress repository.
 * Read this companion article for step-by-step directions on either method.
 * https://www.paidmembershipspro.com/create-a-plugin-for-pmpro-customizations/
 */
function my_pmpro_member_profile_edit_user_object_fields_add_join_date( $user_fields ) {
	// Add field...
	$user_fields['user_registered'] = 'Join Date';

	// Make readonly...
	?>
	<style>
		#user_registered {
			-webkit-user-select: none;
 			-moz-user-select: none;
  			-ms-user-select: none;
  			user-select: none;   
		}
	</style>
	<?php

	// Return.
	return $user_fields;
}
add_filter( 'pmpro_member_profile_edit_user_object_fields', 'my_pmpro_member_profile_edit_user_object_fields_add_join_date' );