My custom page.tpl.php file is not picked up
have you seen through your theme suggestions for the about page?

If not, then please refer to it and create a tpl file according to the suggestions and you will see that particular template running for "about" page.

As of Drupal 7.33, Drupal core has a theme debug mode that can be enabled and disabled via the theme_debug variable. Theme debug mode can be used to see possible template suggestions and the locations of template files right in your HTML markup (as HTML comments). 


  To enable it, add this line to your settings.php:


$conf['theme_debug'] = TRUE;



  OR,
  You can enable it with drush using:


drush vset theme_debug 1



  And disable using


drush vset theme_debug 0


Note: You'll then see output like this when you inspect or view source:

&lt;!-- THEME DEBUG --&gt;
&lt;!-- CALL: theme('page') --&gt;
&lt;!-- FILE NAME SUGGESTIONS:
   * page--front.tpl.php
   * page--node.tpl.php
   x page.tpl.php
--&gt;
&lt;!-- BEGIN OUTPUT from 'modules/system/page.tpl.php' --&gt;
…
&lt;!-- END OUTPUT from 'modules/system/page.tpl.php' --&gt;