Creating new template for new page In drupal 7, I created a content type called page and set the url to /about. If I check the source code I see 

&lt;link rel="canonical" href="/website/about"&gt; 


and 

&lt;link rel="shortlink" href="/website/node/7" /&gt;


So if I create a new template called page--node--7.tpl.php then it works.
But if I create a new template called page--about.tpl.php it wont get picked up.

What am I doing wrong here?

Thanks!
I think you have issue with hook_suggestions that we need to configure correctly for a template to work.

Its already answered here

drupal 7 template suggestions based on path alias

Hope it will help!