Routing in CodeIgniter for (:any)
The routing rule you using it is OK for your purpose.
If you use http://www.example.com/admin/edit_page/3 this link it will send you admin controller and edit_page method.It will not use routes any rule.
However you will get one problem if your link looks like this
http://www.example.com/my-post-example/testIt will try to go my-post-example controller and test method.
Again http://www.example.com/admin will use routes any rule, means it will redirect your to core controller instead of admin/index. In that case your url should be http://www.example.com/admin/index
Finally If you call your other link with controller/method name it will be OK using your any rule