Protect plans older than sign up date minus one week.

membermouse.php

<?php
/**
 * Protect plans older than sign up date minus one week.
 * 
 * This is for a site with new content published weekly;
 * adjust as necessary for other publishing schedules.
 * 
 * @since 1.0.0
 * 
 * @author Travis Northcutt
 *
 */
function gfmp_protect_old_meal_plans() {
	// Do nothing if we're not on a singular post of the correct type
	if ( !is_singular( 'meal-plan' ) ) return;
	
	// how long user has been a member, in days
	$days_as_member = mm_member_data( array( 'name' => 'daysAsMember' ) );
	// publish date of the meal plan
	$plan_date = get_the_date( 'U' );
	// How many days the current plan has been published, rounded down
	$days_as_plan = (int) floor( ( time() - $plan_date ) / 86400 );
	// If plan was published before member joined (plus one week buffer), redirect
	// to the built in Member Mouse error page.
	if ( $days_as_plan > ( $days_as_member + 7 ) ) {
		wp_redirect( "/mm-error/" );
		exit;
	}
	return;
}
add_action( 'template_redirect', 'gfmp_protect_old_meal_plans' );