Ok, I made a little hack for you that gives you the option to sort with the oldest topic start date at the top, and the newest at the bottom:
Open admin_forums.php
Around line 284, find:
<option value="1"<?php if ($cur_forum['sort_by'] == '1') echo ' selected="selected"' ?>>Topic start</option>
After, add:
<option value="2"<?php if ($cur_forum['sort_by'] == '2') echo ' selected="selected"' ?>>Topic start, reverse</option>
Open viewforum.php
Around line 109, find:
// Fetch list of topics to display on this page
After, add:
if (($cur_forum['sort_by'] == '1') || ($cur_forum['sort_by'] == '0')) {
$newsort = 'DESC';
} else if ($cur_forum['sort_by'] == '2') {
$newsort = 'ASC';
}
Around line 117, find
// Without "the dot"
$sql = 'SELECT id, poster, subject, posted, last_post, last_post_id, last_poster, num_views, num_replies, closed, sticky, moved_to FROM '.$db->prefix.'topics WHERE forum_id='.$id.' ORDER BY sticky DESC, '.(($cur_forum['sort_by'] == '1') ? 'posted' : 'last_post').' DESC LIMIT '.$start_from.', '.$pun_user['disp_topics'];
Replace with:
// Without "the dot"
$sql = 'SELECT id, poster, subject, posted, last_post, last_post_id, last_poster, num_views, num_replies, closed, sticky, moved_to FROM '.$db->prefix.'topics WHERE forum_id='.$id.' ORDER BY sticky DESC, '.(($cur_forum['sort_by'] == '1') ? 'posted' : 'last_post').' '.$newsort.' LIMIT '.$start_from.', '.$pun_user['disp_topics'];
Around line 126, find:
case 'mysqli':
$sql = 'SELECT p.poster_id AS has_posted, t.id, t.subject, t.poster, t.posted, t.last_post, t.last_post_id, t.last_poster, t.num_views, t.num_replies, t.closed, t.sticky, t.moved_to FROM '.$db->prefix.'topics AS t LEFT JOIN '.$db->prefix.'posts AS p ON t.id=p.topic_id AND p.poster_id='.$pun_user['id'].' WHERE t.forum_id='.$id.' GROUP BY t.id ORDER BY sticky DESC, '.(($cur_forum['sort_by'] == '1') ? 'posted' : 'last_post').' DESC LIMIT '.$start_from.', '.$pun_user['disp_topics'];
break;
case 'sqlite':
$sql = 'SELECT p.poster_id AS has_posted, t.id, t.subject, t.poster, t.posted, t.last_post, t.last_post_id, t.last_poster, t.num_views, t.num_replies, t.closed, t.sticky, t.moved_to FROM '.$db->prefix.'topics AS t LEFT JOIN '.$db->prefix.'posts AS p ON t.id=p.topic_id AND p.poster_id='.$pun_user['id'].' WHERE t.id IN(SELECT id FROM '.$db->prefix.'topics WHERE forum_id='.$id.' ORDER BY sticky DESC, '.(($cur_forum['sort_by'] == '1') ? 'posted' : 'last_post').' DESC LIMIT '.$start_from.', '.$pun_user['disp_topics'].') GROUP BY t.id ORDER BY t.sticky DESC, t.last_post DESC';
break;
default:
$sql = 'SELECT p.poster_id AS has_posted, t.id, t.subject, t.poster, t.posted, t.last_post, t.last_post_id, t.last_poster, t.num_views, t.num_replies, t.closed, t.sticky, t.moved_to FROM '.$db->prefix.'topics AS t LEFT JOIN '.$db->prefix.'posts AS p ON t.id=p.topic_id AND p.poster_id='.$pun_user['id'].' WHERE t.forum_id='.$id.' GROUP BY t.id, t.subject, t.poster, t.posted, t.last_post, t.last_post_id, t.last_poster, t.num_views, t.num_replies, t.closed, t.sticky, t.moved_to, p.poster_id ORDER BY sticky DESC, '.(($cur_forum['sort_by'] == '1') ? 'posted' : 'last_post').' DESC LIMIT '.$start_from.', '.$pun_user['disp_topics'];
break;
Replace with:
case 'mysqli':
$sql = 'SELECT p.poster_id AS has_posted, t.id, t.subject, t.poster, t.posted, t.last_post, t.last_post_id, t.last_poster, t.num_views, t.num_replies, t.closed, t.sticky, t.moved_to FROM '.$db->prefix.'topics AS t LEFT JOIN '.$db->prefix.'posts AS p ON t.id=p.topic_id AND p.poster_id='.$pun_user['id'].' WHERE t.forum_id='.$id.' GROUP BY t.id ORDER BY sticky DESC, '.(($cur_forum['sort_by'] == '1') ? 'posted' : 'last_post').' '.$newsort.' LIMIT '.$start_from.', '.$pun_user['disp_topics'];
break;
case 'sqlite':
$sql = 'SELECT p.poster_id AS has_posted, t.id, t.subject, t.poster, t.posted, t.last_post, t.last_post_id, t.last_poster, t.num_views, t.num_replies, t.closed, t.sticky, t.moved_to FROM '.$db->prefix.'topics AS t LEFT JOIN '.$db->prefix.'posts AS p ON t.id=p.topic_id AND p.poster_id='.$pun_user['id'].' WHERE t.id IN(SELECT id FROM '.$db->prefix.'topics WHERE forum_id='.$id.' ORDER BY sticky DESC, '.(($cur_forum['sort_by'] == '1') ? 'posted' : 'last_post').' '.$newsort.' LIMIT '.$start_from.', '.$pun_user['disp_topics'].') GROUP BY t.id ORDER BY t.sticky DESC, t.last_post DESC';
break;
default:
$sql = 'SELECT p.poster_id AS has_posted, t.id, t.subject, t.poster, t.posted, t.last_post, t.last_post_id, t.last_poster, t.num_views, t.num_replies, t.closed, t.sticky, t.moved_to FROM '.$db->prefix.'topics AS t LEFT JOIN '.$db->prefix.'posts AS p ON t.id=p.topic_id AND p.poster_id='.$pun_user['id'].' WHERE t.forum_id='.$id.' GROUP BY t.id, t.subject, t.poster, t.posted, t.last_post, t.last_post_id, t.last_poster, t.num_views, t.num_replies, t.closed, t.sticky, t.moved_to, p.poster_id ORDER BY sticky DESC, '.(($cur_forum['sort_by'] == '1') ? 'posted' : 'last_post').' '.$newsort.' LIMIT '.$start_from.', '.$pun_user['disp_topics'];
break;
Save & upload
Now you can sort by topic start in reverse 
