Approach 1: You could assign the role of "editor" to the user, assign the user as author of the three pages and thereafter limit the user to editing only those three pages by following this outlined methodology:
This however does not fulfill your requirement of a dedicated custom admin page. It simply limits what the user can do.
Approach 2: Create a custom admin page as clearly outlined in the codex (http://codex.wordpress.org/Administration_Menus) and fork the code used for listing pages in wp-admin.
Approach 3: Use Role Scoper, a free plugin that allows:
additional Read or Edit access for specific Pages, Posts or Categories
Specify element(s) in Edit Form to withhold from non-Editors
Approach 2, 3 or a combination of 1, 2 or 3 ensures the key to your required functionality.