Comment restrictions Wodpress

The comments_open() boolean function return is filtered by ‘comments_open’. Untested, pseudo code as a guide:

add_filter( 'comments_open', function( $open ) {
    $user = wp_get_current_user();
    $open = $open && $user && time() - mysql2date( 'U', $user->user_registered ) > 3 * DAY_IN_SECONDS;
    return $open;
} );

No guest users will be able to comment either, and I guess that is also what you want.